Yes there is one file at C:\windows\serviceProfiles\LocalService\AppData\Roaming\PeerNetworking
that needs to be delated sometimes > "idstore.sst"
After a few failed attempts at setting up a Homegroup that particular file seems to get stuck and causes corruption of the peerNetworking file which somehow completely kills Homegroup functionality. Glad you got it working.
The interesting part is that I don't even have that file on my machine, absolutely nothing where it supposed to be. Of course Homegroups works perfectly for me also so I would guess that file isn't supposed to be there. God only knows why it was ever created in the first place but I think it's clear that we are dealing with a ligitimate Windows 7 Homegroup bug here.