I recently ran into a similar error with one of my users when they tried to log into Epicor. Searching for a solution, I found the post below and discovered the existence of a user.config file located in C:\Users\username\Local\Epicor\Epicor.exe_StrongName_blahblahblah\IceVersion\user.config. The next time this happens, try renaming that file and opening Epicor and see if it gets recreated and the error goes away and allows your user in.
