Symptoms:

Shortly after opening Outlook you are prompted to enter your credentials.

Cause:

Mail Manager credentials required for online filing locations e.g. SharePoint

Based on the the follow errors:

Error: The partner returned a bad sign-in name or password...

Action: Check user name and password and re-enter correct details when prompted

Error: The remote server could not be resolved...

Action: Check network connectivity to the website

Error: For security reasons DTD is prohibited in this XML document...