How to Fix Dungeon Defenders 2 Fatal Error?

Some Windows users are encountering the ‘Fatal Error’ message whenever they attempt to launch Dungeon Defenders 2 on their Windows computer. This issue is confirmed to occur on Windows 7, Windows 8.1, and Windows 10.

Dungeon Defenders 2 – Fatal Error

After investigating this particular issue thoroughly, it turns out that there are several different potential culprits that might be triggering this particular issue. Here’s a list of scenarios that might directly or indirectly cause the ‘Fatal Error’ when launching Dungeon Defenders 2:

  • Corrupted Unreal Development Kit files – As it turns out, you can expect to see this error message occurring if you’re dealing with a series of corrupted UDK files that are affecting the launch of the game. In this case, you can fix the issue simply by deleting these files manually and launching the game without them (the game is capable of regenerating healthy equivalents of these files).
  • Dungeon Defenders is flagged as a security threat – Keep in mind that you messed around with mods and custom files for Dungeon Defenders 2, chances are your AV will flag the custom files as a potential security threat. To fix this issue in this case, you’ll need to whitelist the main executable of the game.
  • Overprotective Firewall – There are certain situations where this problem can’t be fixed simply by whitelisting the executable. If the 3rd party AV that you’re using includes a firewall component, chances are the only viable fix is to uninstall the overprotective suite to prevent the game from being flagged as a false positive.
  • Corrupted game installation – Under certain circumstances, you can see this error occurring due to some kind of corruption that is affecting the local installation of the game. In this case, the easiest way to fix the issue is to trigger an integrity check on the Dungeon Defenders II game.
  • Shaders on Demand are Disabled – If you’re encountering this issue on a PC with a relatively low-end configuration, it’s possible that the game ends up crashing because Shaders on Demand are not allowed. You can rectify this behavior by accessing the game folder and modifying the BaseEngine.ini file.

Now that you know very potential culprits that might be responsible for this issue, here’s a list of methods that other affected users have used successfully to fix this particular issue.

Method 1: Deleting the Unreal Development Kit Files

As it turns out, the most common instance that might be responsible for the ‘fatal error’ message is a collection of corrupted files belonging to the UDK (Unreal Development Kit) library.

Several affected users have confirmed that the issue was finally fixed after they manually navigated to the location where these files are stored and deleted all of them from the Config folder.

Note: Keep in mind that these files are automatically generated and have regenerative capabilities. This means that even if you delete them and they’re not the source of the issue, the game installation is perfectly capable of regenerating them from scratch.

In this particular case, the ‘Fatal Error‘ is known to occur at the launch of Dungeon Defenders 2 due to the way these UDK files are being distributed within the Steam installation.

One solution around this issue is to navigate to the directory where the UDK files are stored and deleting them manually in order to eliminate the issue:

  1. Start by ensuring that Steam and any game that is launched through the Steam launcher are completely closed and no associated process is running in the background.
  2. Access the File Explorer and navigate to the following location:
    C:\Program Files (x86)\Steam\steamapps\common\Dungeon Defenders 2\DunDef2\UDKGame\Config
  3. Once you’re inside the Config folder, select every file that starts with the phrase ‘UDK’, then right-click on them and choose to Delete to get rid of them.
    Deleting the UDK files from the config folder
  4. After you successfully manage to get rid of every Unreal Development Kit file that’s inside the Config folder, restart your computer and launch the game through Steam once again after the next startup is complete.
    Note: The first time you launch the game after the UDK files are deleted, the files will automatically regenerate.

If you already followed the instructions above to delete the UDK files and you’re still seeing the same fatal error when you attempt to open Dungeon Defenders 2, move down to the next potential fix below.

Method 2: Whitelisting Dungeon Defenders 2 + Steam in AV Settings

In case you previously established that the ‘fatal error’ issue is not being caused by some type of corruption associated with the UDK files, the next thing you should investigate is your antivirus.

Keep in mind that there are a lot of user reports saying that they’ve discovered that the security app was actually responsible for this problem after it ended up preventing the game from using every required dependency due to a false positive- This issue is confirmed to occur with both 3rd party security suites (firewall + antivirus) and the integrated security solution (Windows Defender + Windows Firewall).

If this scenario is applicable, the fix is simple – You need to establish a whitelisting rule in your AV / Firewall that will whitelist both the main executable and the Steam launcher that you use to launch the game.

Note: In case you’re using a 3rd party security suite, the exact instructions for establishing a whitelisting rule will be different from developer to developer. If you can get this done by yourself, look online for specific instructions.

On the other hand, if you’re using Windows Defender + Windows Firewall (the native security options on Windows 10), you can follow the step-by-step instructions below to establish an exception rule for the main Dungeon Defenders 2 game executable and the Steam launcher:

  1. Open up a Run dialog box by pressing Windows key + R. Next, type ‘control firewall.cpl’ and press Enter to open up the Windows Firewall window.
    Accessing the Windows Firewall menu
  2. Inside the main menu of Windows Defender Firewall, go ahead and access the menu on the left-hand side, then click on Allow an app or feature through Windows Defender firewall.

    Allowing an app through Windows Defender
  3. Once you’re inside the Allowed Apps menu, go ahead and click on the Change Settings button, then click on Yes at the User Account Control prompt.
    Changing the Settings in Windows Firewall
  4. After the list finally becomes editable, go directly under it and click on Allow another app, then click on Browser and navigate to the location where the Dungeon Defenders II game is installed.
    Allowing another app inside the list of whitelisted items
  5. Once you manage to find the main executable behind Dungeon Defenders II and added it to the whitelist, do the same thing with the main Steam executable.
  6. Next, find the 2 entries you just added inside the list of Allowed apps and features and ensure that both the Private and Public Checkboxes associated with them are checked.
  7. Save the changes, then launch the game once again and see if the problem is now fixed.

In case you’re still seeing the same ‘Fatal Error‘ even after whitelisting the main game executable + Steam, move down to the next potential fix below.

Method 3: Disabling or Uninstalling the Overprotective AV Suite (if applicable)

If you followed the instructions above to successfully whitelist the main game’s executable + Steam and you’re still encountering the same kind of ‘Fatal Error‘, it’s most likely because the security blockade is enforced by a security rule originating from your firewall settings.

Several affected users complaining about the same kind of issue have confirmed that in their case, the issue was finally resolved after they uninstalled the overprotective security suite.

But before you do that, you should start by manually disabling the real-time protection in your AV settings and seeing if this fixes the issue. Typically, you can do this directly from the tray bar menu by right-clicking on the icon associated with your antivirus.

Disabling Antivirus

In case you already did this and the problem is still not fixed, follow the instructions below to essentially uninstall the overprotective AVC from your computer in order to prevent it from interacting with the launch of Dungeon Defenders II:

  1. Open up a Run dialog box by pressing Windows key + R. Next, type ‘appwiz.cpl’ and press Enter to open up the Programs and Features menu.
    Opening the Programs and Feature menu
  2. Once you’re inside the Programs and Features menu, scroll down through the list of installed programs and locate the listing of the antivirus suite that you plan on uninstalling. When you see it, right-click on it and choose Uninstall from the context menu that just appeared.
    Uninstalling the problematic antivirus
  3. Inside the uninstallation screen, follow the on-screen prompts to complete the uninstallation procedure, then restart your computer and wait for the next startup to complete.
  4. After your computer boots back up, launch Dungeon Defenders II once again and see if the problem is now fixed.

If this method was not applicable or you already follow the instructions below and you’re still encountering the same kind of issues, move down to the next potential fix below.

Method 4: Verify the integrity of Dungeon Defenders II via Steam

According to several affected users, you can also expect to see this issue if you’re currently with some type of corruption-fueled inconsistency that is affecting the local Steam installation of Dungeon Defenders II.

If this scenario is applicable, you can fix the issue by forcing the Steam application to run an integrity check on Dungeon Defenders II – This procedure will automatically scan every game file and replace every corrupted item with a healthy equivalent.

Note: Before deploying this particular fix, it’s important to ensure that you have a stable internet connection.

Follow the instructions below to trigger an integrity check on the Dungeon Defenders II files:

  1. Open up Steam conventionally with admin access, then access the Library menu from the tab at the top.
  2. Next, from the list of games, right-click on Dungeon Defenders II and then click on Properties from the context menu that just appeared.
    Accessing the Properties screen of the game
  3. Once you’re inside the Properties screen of Dungeon Defenders II, access the Local Files tab, then click on Verify Integrity of the Game file.

    Verifying the integrity of the game
  4.  Confirm the operation when asked to, then wait for the process to complete before launching the game again to see if the startup error has stopped occuring.

In case you’re still encountering the same ‘fatal error‘ startup prompt even after checking the integrity of the game, move down to the final potential fix below.

Method 5: Modifying the BaseEngine.ini File

As it turns out, you can also expect to see the ‘Fatal error‘ to occur when launching Dungeon Defenders II due to a graphics technology that is unable to force Shaders on Demand in situations where the game is rendered on a low-end PC configuration.

Fortunately, several affected users that were encountering this issue have confirmed that they were able to fix the issue by navigating to the location of the game and edited the BaseEngine.ini file from the Config directory.

After replacing the value of bInitializeShadersOnDemand from False to True, most affected users have confirmed that the issue was resolved and they were able to play the game normally.

Note: In order to be able to modify the .ini file, you will need a competent text editor that opens with admin access. In these types of situations, we prefer to use Notepad++

If this scenario looks like it could be applicable, follow the instructions below to modify the BaseEngine.ini so that it allows the usage of in-demand shaders:

  1. Ensure that Steam, Dungeon Defenders II, and any associated process is closed and not running in the background.
  2. Visit the official download page of Notepad++ and click on the Download button to download the latest version of this text editor.
    Downloading Notepad++
  3. Once the download is complete, double-click on the installer and follow the on-screen prompts to install the text editor on your computer.
    Installing Notepad++
  4. After Notepad++ is successfully installed on your computer, reboot your system and wait for the next startup to complete.
  5. Open File Explorer and navigate to the location where you installed Dungeon Defenders II. By default, the game is installed in:
    C:\Program Files (x86)\Steam\steamapps\common\Dungeon Defenders 2\DunDef2\Engine\Config
  6. Once you manage to arrive inside the correct location, right-click on the BaseEngine.ini and choose Edit with Notepad++ from the context menu that just appeared. When you’re prompted by the UAC (User Account Control), click Yes to grant admin access.
    Editing the file with Notepad++
  7. Once you have an overview of the contents of the BaseEngine.ini file, scroll down and find the following line of code:
  8. After you find the correct line of code, change the value from False to True and hit the Save button after you confirm that the line now looks like this:
  9. Start Dungeon Defenders II conventionally (through Steam) and see if the issue is now fixed.

Kevin Arrows

Kevin Arrows is a highly experienced and knowledgeable technology specialist with over a decade of industry experience. He holds a Microsoft Certified Technology Specialist (MCTS) certification and has a deep passion for staying up-to-date on the latest tech developments. Kevin has written extensively on a wide range of tech-related topics, showcasing his expertise and knowledge in areas such as software development, cybersecurity, and cloud computing. His contributions to the tech field have been widely recognized and respected by his peers, and he is highly regarded for his ability to explain complex technical concepts in a clear and concise manner.