Using New Outlook on Windows for professional communication and productivity
Hello! My name is Ben a fellow member here in the community, not a Microsoft employee. Hope you are doing well!
I see you have an error here in adding your MSN.com account to the new Outlook for Windows app. The issue could be on the version of the app you are using.
As for the troubleshooting steps you can try, you can follow the post on the community forum here below to perform the troubleshooting steps posted by Mia.W:
https://answers.microsoft.com/en-us/outlook_com...
The one that worked for one of the members is to change the name of the OLK folder following the path: c:\Users\YOURUSERNAME\AppData\Local\Microsoft\Olk
You can actually try the steps as well and feel free to post back here in the community on how it goes so we fellow members can share our knowledge further and help.