Error starting MR - "Your application settings file (user.config) appears to be corrupt..."

We have AX 2012 R2 and MR 2012 CU11 deployed on Citrix XenApp 6.5. Occasionally some users will get the following error message when they try to start Report Designer:

"Your applications settings file (user.config) appears to be corrupt. Reinstall the application to repair the file" error message.

Simply killing the Citrix session always resolves the issue. Does anybody know the actual cause of this error message and the way to permanently fix it?

Thanks, Milan