Outlook keeps prompting for password

Good Article at Technet

Outlook keeps prompting for password could be caused by several reasons:

• Outlook is configured to prompt you for credentials
• Incorrect password cached in credential storage
• Required Authentication Settings for outgoing server and incoming server
• Outlook Anywhere is not configured to use NTLM Authentication
• Corrupt Outlook profile
• Slow or unstable network connection
• Antivirus programs
• Shared calendars

A forum article discussed this issue in detail, please follow the instructions in the article to troubleshoot the issue:

https://social.technet.microsoft.com/Forums/en-US/bcd2d9c2-1a1b-4446-bf32-69fee8cdf11b/why-does-outlook-keep-prompting-for-password?forum=outlook