I'm getting the error "Disconnected due to port error" on the log screen.. [edit] i'm not behind any firewall or router either...
I don't wanna burst your bubble here, but even with the helpful hints from soveryshiny, i guess you're screwed... :|
Your symptoms probably mean that your Internet service provider has some of those high end Cisco firewalls on their side, that can automatically drop the connections to most of the p2p sharing systems...
I should know, i have the exact same issue.
On my work computer using the main ISP acces, Share disconnects after a few seconds...
On the same computer using the backup access (not the same ISP), Share works just fine... (but, the backup access sucks in term of speed, so i can't really use it anyway).