Credentials conflict

We just installed a new server running win2k server. We established a new domain name for this server. There are 16 win2k pro workstations attached to this server. after joining all the wrksta to the domain I had to do a clean installon 2 of them. When I tried to join them to the domain again I got the message “credentials supplied conflict with existing set of credentials”. I tried to give the computer a different name. I’ve deleted the computers from the server. I still cannot join the domain. What am I doing wrong?