Active Directory uses SRV records in DNS for locating domain controllers so users can log on and so on. But if something goes wrong and your DNS database becomes corrupted, these records can be difficult to recreate.
Joeware has come to the rescue here with a new utility called DNSSrvRec that you can use to create and delete SRV records easily. You can download this utility for free from http://www.joeware.net/win/free/tools/DNSSrvRec.htm