If you encounter this error (and haven't seen the workaround on other blogs), please make sure you have these updates installed on the Hyper-V hosts:
Hyper-V QFE (KB956589)
BITS QFE (KB956774)
PingBack from http://mstechnews.info/2008/11/needs-attention-status-on-scvmm-2008-rtm/
You might want to mention what update is needed for Virtual Server 2005 as well.
You might want to mention what update is needed for the same problem under Virtual Server 2005 on Windows 2003 as well.
Remove and then re-add the Host worked for me...have you tried that?