Recently I built a virtual domain environment and ran across a small issue. My plan was to build two seperate servers. The first server I built was an AD domain controller and the other my SMS server. I ran across an issue when I copied the first vhd file over too a new location and tried joining that PC to the newly created AD server.
It turns out that even though both machines had a different name the SID (Security Identifier) was the same. To resolve this issue I ran a free tool called NewSID which can be found here.