Can't access WebService on WinServer2003

[QuocSI]

I've deployed and run a WebService on Windows2000 without problem.
The same one installed on WinServer2003 expect an authentication.
Everything I've done don't run (changing autentication method, impersonate
user, ...)

WindowsServer2003 don't give me access to my WebService.
Where can i change the Security Strategie to obtain access to my Webservice.

Thanks a lot for your help

Bye