Can’t raise functional level of DC

I have a Server with 2003 Ent sp2. I have to rename the domain but need to raise it’s functional level to 2003.

When I try and raise level of the Forest, I get: “The functional level cannot be raised, the directory is busy”

When I try to raise the domain, I get the same message.

I have rebooted the system and tried this with no clients logged on.

Any ideas?