How to Fix Outlook 2007 Keeps Prompting for Username Password When Using Outlook Anywhere
If you are using Outlook 2007 to connect to a Microsoft Exchange 2007 or 2010 server using Outlook Anywhere (formerly know as RPC over HTTP), you may have a username/password box constantly popping up asking you to enter your credentials. This will continue to happen even after entering the correct username/password and checking the "Remember my password" box:
If you get the same username/password box, but the "Remember my password" box is missing, you must first upgrade Office 2007 to SP3. Update through Windows Update, or download the service pack directly here.