Ever run into a problem where you revert a domain member server or Windows XP domain client toa previously taken snapshot, and when trying to log on the domain, the logon fails?
I did in 2007, and never really thought of it until I ran into the following article on the VMWare knowledge base: http://kb.vmware.com/selfservice/viewContent.do?externalId=1006764&sliceId=1
The cause is very simple, and so is the solution: Member servers and clients have, just like users, accounts with passwords. If set up like this, these passwords are reset every set period. If you revert a machine back to an old snapshot, chances are that the password stored in the snapshot is not up to date with the password stored in Active Directory, and hence, Active Directory does not allow the machine to log on again.