One of my colleagues got this same issue yesterday on his Epicor SI image laptop. This happened on the Administrator account.
Reinstalling the client did not help, so I went to look at the user.config on the path mentioned on the error message, and the file content was empty. The file got corrupted somehow…
My solution was to copy the text content from a valid user.config file (different user) into the one corrupted. That worked for us.
Carlos Quintanilla
PSE