The Host status of 'Not Responding' in SCVMM 2008, status indicates that the VMM server is unable to communicate with the Host for some reason. If this communication is interrupted for any reason, even intermittently, then you can expect the Host status to change in the VMM admin console. The first item to check is to make sure that the following hotfixes are installed: 958124, 954563, 955805, 961983.

Full Article: SCVMM blog