i have two computers running windows 7 64bit. i have been using homegroup and shared folders for some weeks without problems. Then suddenly i couldn't access the shared folders or the homegroup. I tried a lot of things; turning off\on firewall on the router, changing logon passwords on the computers, changing different settings, changing workgroup name, etc etc etc... and I uninstalled Avast free antivirus, and now i can connect again. Could it be Avast free antivirus that caused the problem? (i think the problem started around the time i installed it) I tried so many things that i haven't a clue what made the difference. If Avast is known to make problems for HomeGroups, does anyone know why? and is there something i can do to still be able to use it? And are there some antivirus that doesn't make problems for homegroup\folder sharing?

As you have found out the cause (Avast), you can check if there is any network related settings on it.If it is not the last version, try get the newest one to see if issue still exists. And there is a free antivirus program released by Microsoft. You can find it here.