Error 0x800c0155 followed by a few digits is caused usually due to permissions with the WLM Message Store.
The complete error message would be similar to “Windows Live Mail could not be started. The application was unable to open the Windows Live Mail message store. Your Windows Live mailbox data is currently being used by another program such as a virus scanner. Close the program or wait for it to complete its operation, then open Windows Live Mail again. (0x800c0155,2)”
The issue can be fixed, but it is important to understand what may have caused it first to avoid it from happening again. Permissions are usually changed by other third-party programs; such as cleaning programs, mailwasher pro etc.
I beleive you know it better then i do on what was ran on your system before the issue occurred. In order to fix the issue; follow these steps below.
Method 1: Change Permissions on the MessageStore
1. Hold Windows Key and Press R
2. Type %appdata%
3. Click OK. And look at the Folder Paths on the top, it should be “Username” -> “AppData” -> “Roaming”
4. Click “AppData” to go back one folder.
5. Choose Local and then Choose “Windows Live Mail”
6. Locate Mail.MSMessageStore and right click on it -> Choose Properties
If you cannot see this folder, make sure that the attribute is to show “hidden files”. If you don’t know how, check this guide
Then choose the Advanced tab and select the Owner Tab
7. Click Edit -> then click Other Users or Groups
8. Type your username in the box and click Check Names, it will automatically search for it. If you do not know your username, then you can check this by click Start on Windows 7, the username should be displayed above the Documents folder in the right side folder’s tree.
9. Once you have your username there, click OK/Apply/OK.
10. Exit out of it, and now try re-opening Windows Live Mail.