@Titus Emanuel when users cleared their cache under "%USERPROFILE%\AppData\Local\IsolatedStorage", they are able to log-in again.
Before performing this work around can you give us the following information so that we can try to address this isue?
- Operating system version
- Previous TBC version
- Current TBC version
- How did they upgrade TBC?
- Was the issue observed after the upgrade immediately? or after re-login TID?