This worked for me:
- Go to your users folder (e.g. C.:\Users\John).
- Right click, select properties, Security, Advanced.
- ClicClick Add, select entity, advanced, search.
- ClicClick on ALL APLICATIONAPPLICATION PACKAGES, accept. Select Full Control and apply (Ignore errors trying to aplyapply permissions).
Then:
- Click on start and type “Services”.
- Right click on “Services” and select “Run as Administrator”.
- In the Services Window, look for Credential Manager Service and “Stop” it.
- Restart the computer and “Start” the Credential Manager Service and set it to “Automatic”.
- Restart the computer and it should work fine.
Source: http://answers.microsoft.com/en-us/windows/forum/apps_windows_10-outlook_mail/cant-add-gmail-account-to-windows-10-mail-app/97d4e308-54a8-4afe-b74f-501b1ea0fa2a?page=12https://answers.microsoft.com/en-us/windows/forum/apps_windows_10-outlook_mail/cant-add-gmail-account-to-windows-10-mail-app/97d4e308-54a8-4afe-b74f-501b1ea0fa2a?page=12