One of our clients is suddenly experiencing this issue in their office and we aren't sure what is going on. What should we do?
@JustinC12: Error 6151 indicates that there is a problem connecting with the authenticating authority. To troubleshoot this issue: First of all ensure that the RDP server and AD can ping each other Secondly, make sure that the trust configuration between the AD that should authenticate the login and the RDP server is configured correctly. In some cases, the RDP server loses domain trust. In that case, it can be fixed by simply rejoining (switch to workgroup and join again) the server to the AD.