The most common issue people are having is when they disconnect or unplug the AC Power Cord it results in a runtime pop-up error related to atibtmon.exe. Atibtmon.exe is a ATI Brightness Monitor Program.
When you disconnect the AC Power Cord it signals this program; which returns the error if it cannot make the changes it is supposed to such as dimming the brightness and switching to a low-power mode to save energy and increase the battery’s runtime.
Many reasons for this to occur; but my guess is that the software crashes and this could be due to upgrade or compatibility.
In order to fix the issue; open the Catalyst Pro Control Center and choose “PowerPlay” under the Power option from the left pane.
Then uncheck to disable “Vari Bright” and hit Apply.