It sounds to me like it is a permissions problem. The file is read only.
Go to both the AC folder on THAT computer, right click and look at sharing and at permissions. Make sure that "Everyone" (to keep it simple) has read/write permissions. I would then check the file user.dic and see if everyone has read/write permissions. Just to be safe for now, give them all FULL permissions.
Given the error message, this is likely your problem.
