It is common for individuals to encounter error messages on their computer screen that state "Sorry, another account from your organization is already signed in on this computer" each time they attempt to open and sign in to an Office 365 application that is installed on their Window's PC. In order to resolve this specific issue or any other Office 365 sign-in issue, the following are two methods that individuals can employ in order to correct their issue:
Solutions for Windows PC
Method #1 for Windows PC: Clear all cached account credentials (i.e. usernames and passwords) related to your Mason Office 365 email account (i.e. NetID@gmu.edu):
1. To clear the account credential cache, first quit all Office 365 applications (Outlook, Teams, Word, etc.) on your device. Next open Credential Manager and remove all credentials related to Office 365. To locate the credential manager, click on the Window's icon in the bottom left corner and type into the search bar Credential Manager. 
2. Moreover, you can also locate it by visiting Control Panel > User Accounts > Credential Manager.
3. Once Credential Manager has been opened, click on Windows Credentials and scroll down to Generic Credentials. Under Generic Credentials is a list of all cached account credentials on your device. Remove all cached credentials related to Microsoft Office 365 accounts (see image below):
4. After you have removed the credentials, restart your PC and attempt to sign in to your desired Office 365 application (i.e. Outlook, Word, Teams, etc.)
Method #2 for Windows PC: Remove your Mason account from your Windows PC:
1. If the steps in the first method above did not resolve your issue, removing your George Mason University account from your PC might be able to resolve your issue. To remove your account from your device, first, click on the Windows start icon in the bottom left corner of your screen then open the settings page.
2. Once the settings page has been opened, click on Accounts > Access work or school. Right-click your Mason NetID and click "Disconnect" to remove the account from your device 
Solution for Apple Mac Devices
Method #1:
1. Click on the search option (the magnifying glass icon) and search for "Key Chain Access"
2. Once you have opened the Key Chain Access page, click on the search option in the top right corner and type "Office 365". Once the search entries have appeared, delete each one, restart your device, and attempt to access your preferred Office 365 application again.
