Had this happen at a clients today…

Multiple connections to a server or shared resource by the same user, using more than one user name, are not allowed.

I tried “net use * /d”… I checked DNS settings… that didn’t help.

In my case, my client had the same administrator:password login, both on the local machine, and as the domain account. So, even while the computer was disjoined from the domain, the local admin account had rights to the server. This defeated using the server credentials when trying to add the computer to the domain. Changing the local administrator password to something else solved the problem.