Have you read through this?
Connection problems? Check here first!
Do this test & see if it works
http://www3.limewire.com:6346
There are a few hints that Atlantic may be using traffic shaping for p2p but nothing to say that they're actually blocking. Have you tried using any other p2p apps & if so, do they connect? You could try changing to a higher port
Alternative Ports
If you're using port forwarding, you'll have to change that for the new port number. You'll also have to change port numbers within your software firewall configuration