Hi,
I wasn't a member of a Homegroup, but still had the problem....
After joining the Homegroup and then leaving, disabling, whatever, my sleep is working properly...
I have read elsewhere that if all of the machines on the Homegroup are not configuerd the same, this issue will occur...
The fix, as mention in another reply, was to remove all of the machines from the Homegroup, and restart them. I would imagine all at the same time if possible...
I have made no changes to my router, adapter, or whatever, and the Sleep has been working properly for 2 days now.