The problem was resolved (gone) for me after a restart of the machine that wouldn't accept the file sharing request (it could 'see' others, but they couldn't connect to it). Good luck.
Same problem as original poster. In Terminal, I can ping the machine that won't connect in the Finder. I have firewalls off (Apple Menu > System Preferences > Security > Firewall tab > "Allow all incoming connections" selected). Any other suggestions?
