I have a user on our organization that uninstalled office 365 on her computer but didn't realize that she hadn't signed out first. She reinstalled and now gets the error of another account from this organization is already signed in. Therefore, she cannot use Office 365. If she uses Teamviewer from home to try and work, she gets the same message. If I log her in on my computer at work as a test, it is fine. The problem occurs if she trys to access Office 365 from her How do I clear that message from her computer so she can work? She is desperate! She hasn't been able to work in 3 days.
