credential conflict w2k

Running w2k Advanced Server single domain – just in the last week a problem has developed when changing the computer name or joining w2k workstation computers to my network:
After choosing to join the domain from the workgroup computer and enteringthe only administrator name and password that we have,I get an error message: “The credentials supplied conflict with an existing set of credentials”
I searched technet briefly and couldn’t find an answer.
Please Help!