A useful command-line way to remove and re-install the Hyper-V 2008 R2 virtual switch protocol has been provided in the past but the reinstall no longer worked for the SP1 release. Here are the two command-line tools:

Remove (obviously unchanged in SP1)

netcfg -u vms_pp

Reinstall (changed in SP1)

netcfg -l C:windowswinsxsamd64_wvms_pp.inf_31bf3856ad364e35_6.1.7601.17514_none_c10b98cd0801eba6wvms_pp.inf -c p -i vms_pp

Reinstall (pre-SP1)

 netcfg -l C:windowswinsxsamd64_wvms_pp.inf_31bf3856ad364e35_6.1.7600.16385_none_beda85050b13680cwvms_pp.inf -c p -i vms_pp