I hate it when users continually receive a pop-up from Outlook 2007 requesting to input their username and password. Yet they put it in and it keeps coming up!
First check any administrator should make is to confirm that the user’s account is not locked out. Check. User is not locked out. Maybe their password expired? You can have the user change their password or force them to change it. If that doesn’t work then we have to walk over to their desk 
We have Sharepoint tied into our users’ Outlook inbox. So I figured if all the credentials are correct, it must be a Sharepoint issue. That was exactly the problem!
A while back we had to rebuild our Mysites and it looks like the user had somehow got a copy of the old My Site documents folder and a copy of the new one. I had him remove the original copy since that was the old Mysites and voila! His Outlook credential pop-up screen was solved.
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- Find Your Mailbox Size in Outlook 2007
- How To Fix Outlook 2007 Instant Search From Not Working
- Exchange 2007 & Backup Exec 12d Failed Backups
