Ok I have posted a similar problem, in this site recently. I added a test user to my group policy to deny access to a specific computer on a computer workstation. I got it to work so that I would get the following error message when I tried to log on to that account
Getting error the signin method you're trying to use isn't allowed.
Once I tested this. I removed it from the policy and now the policy is not defined. However I am still not apple to logon to the computer using the test user. I can logon as any other user, but that one.
I have done a gpupdate on the server, restarted the server and I also have done a gpupdate /force on the workstation computer. I have also tried restartimg the workstation computer but nothing seems to work.
Using windows server 2012 r2