While trying to access Outlook Office 365 one of the users was getting the below error.
Exchange online licenses were assigned to the user, and also the other users were not facing this issue.
As suggested in one of the forums, we tried re-assigning the license.
i.e. Unassign and reassign the license to the user.
We kept getting the issue (even after trying in different browsers and also in in-private browsing).
We tried the same after 1 hour or so and the user was able to access the outlook office 365, seems like the change takes time to propagate.
So the key is to make sure the licenses are active and appropriately assigned and followed by a little bit of patience.
Hope it helps..