If outlook keeps popping up asking for credentials and your using an Office 365 account, try this:
Click here to run the Microsoft Office 365 Support and Recovery Assistant.
Select Outlook > then “Outlook keeps asking for my password“. Follow the instructions in the wizard and this should resolve the issue.
If you have tried to create a new mail profile, or have deleted your mail profile you may be getting this message. The above steps should still resolve the issue.
Error: Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. You must connect to Microsoft Exchange with the current profile before you can syncronize your folders with your Outlook data file (.ost).