Installing Exchange Server 2000

Everytime I attempt to load Exchange Server 2000 I receive the following error in the log during installation “Extending the schema in active directory failed.Lidff.err” I downloaded the IntOreg and loaded the modules but receive the same error. I have the proper permissions for domain admin, enterprise admin and schema admin added to user on the server. I even edited the registry to allow the schema to update. Does anybody have any ideas???