Had this happen to me and its easy to overlook. Make sure you don't have a cached account name in the account box. In my case somehow and oldcomputername\account (or olddomain\account) was in the rdp cached credential box and it was giving this error. Instead of using command line to login, used the ui, click on show options and changed username to .\account and was immediately prompted for the password and was able to login.
Hope this helps.