forest prep errors

I am getting the error that “either you do not have permission to update the active directory schema or active directory service is currently too busy”. I got this error on the dc when trying to run it. Our network consists of the dc which is the forest root, and a member server which will be the exchange server. I get a similar error on the exchange server. I found some suggestions to look for, but none have worked so far. Remote registry is running, my user is the same one we used to install windows and has schema and enterprise level permissions. I did run dcdiag and get an error that the rpc server is unavailable. Could that be the cause? Any help is appreciated!