I've been stuck on this for a while, not sure what permission I'm missing. I've got domain A and domain B, A trusts B, but B does not trust A. I'm trying to run a service in domain A with a user account from domain B and I keep getting Access is Denied. I'm using the FQDN after the username and the password is correct. The user account from domain B is a local administrator on the domain A server, the user account has the logon locally, and as a service permissions. Must. Get. This. Working. Update: I found something interesting in the logs I must have missed. This ought to get me pointed in the right direction. Event ID: 40961 - LsaSrv : The Security System could not establish a secured connection with the server ldap/{server fqdn/fqdn@fqdn} No authentication protocol was available. I've found a few fixes for 40961 but nothing has worked so far. I've verified reverse lookup zones. nslookup resolves the correct dc properly. still workin' at it. Upadte: In response to Evan; I ran " runas /env /user:ftp_user@fqdn "notepad" " then entered the users password and notepad came up. It seems to work successfully. This issue is now resolved. The problem is visible in the screenshot. Windows tries to use the UPN for the user account if you dig your user out of AD with the Browse button. This fails every time even with the right user and password. Simply using the SAM format (Domain\User) works. So simple, yet so annoying. Can't believe I missed this. Thanks to everyone who helped.