I'm feeding this into Google, in case anyone else ever runs into this problem that I helped someone fix with their domain this week: If you have taken down one domain controller for maintenance, and then you attempt to add it back into your domain after a rebuild, and you encounter the error "Network path not found", you have a problem. This error usually means that you have some sort of DNS problem, but if you double-check all your TCP/IP settings, and find that's not the case, there's one more thing to check.
Check to make sure someone hasn't disabled File and Printer sharing on your "backup" domain controller. Without that enabled, Active Directory will NOT function properly. Go into the Network control panel, re-enable that protocol, and you're in business.
I know, this is a pretty obscure problem, and most people wouldn't accidentally disable file and print sharing on a domain controller, but it's possible (and baffling at first) so that's why I'm sharing.