Workstation joining a domain

I’m trying to add a workstation to our local domain, however everytime I try to add it i get the following error.

“Your computer could not be joined ot the domain because the following error has occurred:
The credentials supplied conflict with an existing set of credentials.”

I’ve double checked the computer name, user account and domain and nothing that I can see is conflicting.

I’ve also checked on the Microsoft Knowledge Base with no luck, any help would be greatly appreciated.

Michael