I have always been trained that it is essential that every computer on your network MUST have a unique SID (Computer Security Identifier). In today’s world of re-imaging computers, changing the SID is always the first step taken. I have a post that discusses using NewSID to easily change the SID on a server.
NewSID is a small executable that will reset your SID. It gives you the option to set a random SID, copy a SID from another computer or specify the SID. It will also allow you to change the current computer name.