Outlook keeps prompting for password but delivers emails

Issue

Microsoft Outlook 2010 connected to Exchange 2007 mailbox on a local LAN network.

User keeps getting Outlook password prompt. Entering correct credentials removes the prompt for a few minutes, but then it reappears. Incoming and outgoing emails are working fine.

Resolution

The issues was caused by expired user’s network (Active Directory) password. After the user logged off and tried to log back on, he was prompted to change the password, which resolved the problem.

Windows Small Business Server (SBS) 2008
Windows 7 SP1
Microsoft Outlook 2010 SP2