I am experiencing a very similar problem as RobinB. I am using workgroup file sharing. The workgroup works. I can access files on my XP64pro from my Win7x64 machine (has Avast! 7 Pro), but not vice-versa. Going manually in “Run” to \computername\sharename does not help. What makes two-way communication immediately possible is disabling the Avast! shields. This makes me certain that the nework and workgroup are properly configured; it is Avast! preventing the communication. Funny thing is, I have a Vista32 machine running Avast! - no problems between it, the Win7x64, or the XP64pro machine. Only the XP64pro connecting TO the Win7x64 machine is a problem. I have set the firewall to “friend” the IP addresses in my local network. I have enabled windows file sharing in the firewall - no luck. One last weird thing - I can see the Win7x64 machine on the list of workgroup computers (on the XP64pro machine), just cannot connect to it. Don’t really expect any answers, just wanted others to know that the problem is real and Avast! is the problem.