Some users are still reporting this issue.
If you are affected, please contact our Support team for assistance.
You may be able to resolve this issue yourself by following these instructions:
1) Quit Outlook and all other Office applications
2) Open Credential Manager in Windows or KeyChain on Mac OS
3) Remove ALL credentials for any of these entries:
-outlookanywhere.horizonpacific.com
-Your email address(es)
-Generic Credentials for: Microsoft, Office, Outlook, Exchange,
4) Install all available MS Office updates
5) Start Outlook and enter and save the users username and password for your exchange account again
6) See if the prompt is cleared or returns

Update

• We believe this issue is resolved
• We are awaiting reports from in the field since we are unable to replicate this issue ourselves
• We believe this issue was caused by a mis-configuration of services within our hosted exchange email system that occurred sometime within the last 30 days

Next Update

• Next Monday at 4PM or sooner

• We are actively seeking a resolution to this issue