Apparently when installing a new Exchange 2007 SCC cluster, you can’t give the resource group containing the physical disks the same name as what the cluster virtual name will be.
For example if your mailbox virtual server will accessible via shortname “vmbx01”, calling the cluster group “vmbx01” will result in setup failing with this error:
Cluster Common Failure Exception: Cluster Common Failure Exception: The group or resource is not in the correct state to perform the requested operation. (Exception from HRESULT: 0x8007139F)
Once I renamed my cluster group to “vmbx01-disk”, setup proceeded business-as-usual. After setup completes you need to migrate all the disks to the new “vmbx01” cluster group that setup will create. This is documented in this article starting at step 19: http://technet.microsoft.com/en-us/library/bb123969.aspx.