Tony,
I got the same problem on a 2003 SP1 Server...
If you check the AWS 6.2 documentation, you see that the suported operating systems are Win 2000 SP3 or 2003 (native)...
The 2003 SP1 has introduced a series of new security updates which conflict with AWS 6.2 credential validations. The only solution I got was to remove SP1 from the Win 2003.
I know it's a security matter, but it worked.
Check if SP1 is applyed to your OS.
Regards.