Since you are connecting from work, Stief's suggestion sounds good. They may have detected extra bandwidth used & put a block on staff using internet for p2p sharing. They may have used a blocker program or simply closed off ports. Try changing the connection port to one between 49152 - 65535; a good one to try is 64049. To change connection port, go to LW's preferences (keyboard shortcut: ⌘ ,) & choose Advanced -> Firewalls. You will see options for connection port & listening port. Try changing both. Also check your OSX firewall to make changes; OSX Firewall settings for Tiger & add the appropriate port or range of ports.

It seems port 6346 is being totally blocked. Question is how & why, & if there are other options or ways of unblocking it.