With the recent update of Hyper V RC1 SCVMM 2008 BETA now longer was compatible. This was due to new functionality and differing screens within the GUI
This week Microsoft have released a patch for SCVMM 2008 BETA to support the functionality of managing Hyper V RC1 hosts via SCVMM.
Download the small patch and install on your SCVMM server.
Once you have installed this update, it cannot be removed.