I am adding a Windows 7 x64 computer system to a 2012 R2 Essentials domain via the connector (http://server/connect) and it just sits and spins forever. Some digging around, I found that removing items in HKLM\SYSTEM\CurrentControlSet\ControlSessionManager\PendingFileRenameOperations and rebooting then reattempting to add the computer works.
Server 2012