How to solve error "Sorry, Another account from your organization is already signed in on this computer" when signing into Excel

Situation

You get a pop-up window asking you to sign in with an Office 365 account. After you fill up your Office 365 credentials, you get an error message saying "Sorry, Another account from your organization is already signed in on this computer".

Solution

This solution works for all office desktop apps like Word, Excel and PowerPoint.

1. Close all Office Apps, Skype for Business, Teams, and Internet Explorer. Use Task Manager to check that all these apps are closed.

2. Clear your credentials.

a. Click the Start button and type Credential Manager then click on it

b. Click the Windows Credentials tab

c. Expand every item one by one and select Remove

3. Clear your Office identity from the Registry.

a. Click the Start button and type Regedit, then click on it

b. Delete both of the following entries:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity


HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Registration

4. Delete your license data.

a. Delete the following folder and all of its contents
%localappdata%\Microsoft\Office\16.0\Licensing\

5. Reboot your computer.

6. After your computer restarts, launch Excel and attempt to sign in with your Office 365 credentials. If the error message still shows up, repeat steps 1 to 4 and continue to step 7.

7. Add two registry entries. 

a. Click the Start button and type Cmd, then click on it

b. Enter these two commands to add in ADAL WAM OVERRIDE:

REG ADD HKCU\Software\Microsoft\Office\16.0\Common\Identity /v EnableADAL /t REG_DWORD /d 00000000 /f 
REG ADD HKCU\Software\Microsoft\Office\16.0\Common\Identity /v DisableADALatopWAMOverride /t REG_DWORD /d 00000001 /f

8. Reboot your computer.

9. After your computer restarts, launch Excel and attempt to sign in with your Office 365 credentials. 

Credits to Urtech.ca