I have the same problem mentioned above with 2.1.3 after an upgrade from 1.7. just wanted to add my weight...
I had no problem before, even when running purely NAT'ed (though obviously I could not upload then). Now it either doesn't work at all (tries for ever getting 'waiting for x busy' and then eventually gives up 'Could not download') or (once so far) it works fine. Bizarre
My specifics: running WinXP on a fairly fast machine, behind an Alcatel Speedtouch 510 ADSL router, running NAT. I've port forwarded 6346 to my desktop, and forced my IP to the real external address. Obviously, I am also not downloading from private addresses.
I also noticed the Windows command line stuff is really slow when Limewire is running (eg. command prompt, telnet etc.). Not sure if this is related, or if it did this with 1.7.
Someone must have an idea?
Andy