I have been banging around HomeGroup for a couple days and so far I have found that if IPv6 is disabled in the network properties (of which I have disabled for many moons), another system cannot join the group (through that computer).
I have not figured out exactly if that is the only requirement or not.
Another thing, If the system is already part of a HomeGroup and the HomeGroup services are disabled, you cannot leave it. Makes sense there.
The other services, mainly related to Peer to Peer and IPv6 are needed a bit of looking at to see what exactly is needed for this to function fully.
More research needed. Stay tuned.
