Since the upgrade of Exchange 2010 from SP2 to SP3 and running office 2010 x64 on Windows 7 x64 I notice that outlook keeps prompting a handfull of users for their username and passwords. Some of the culprits I have picked up are as follows:

• Windows 7 Credential Manager is not updating the information when a user updates their domain passwords.
• Outlook 2010 is not set to NTLM password authentication.
• In a hidden folder, Outlook stores multiple folders with passwords, if removed it prompts once and not again.

To fix the above, simply update credential manager with the new password, if you look at the date it will show when last it was updated.

Change the authentication for outlook to NTLM, close and open outlook.

Remove all the hidden folders and let outlook create them again.

Some might say it is an autodiscover issue but if you hold down CTRL and right click on the outlook icon next to the clock in the taskbar and test Email AutoConfiguration it should show the correct URL’s, if not then their is your problem.

Hope it helps.