In my domain NC, my wellKnownObject for the default computers container (GUID_COMPUTRS_CONTAINER_W) was missing. Not sure why, but I was unable to join a Windows 2008 R2 server as a domain controller because of this. Perhaps dbcheck should check for missing wellKnownObjects. I believe that there are checks for missing object values/guids, but no check if an entire wellKnownObject is missing (or if so, dbcheck didn't find it in my case).