My guess is you need a fresh connection file. I do not have a Linux installer for this but you can download the file and place it in the right location yourself.
See half way down this post where it says * Note: http://www.gnutellaforums.com/other/...tml#post359417. An alternative gnut file can be found here.

Just a note, all LW 5 versions including LPE will delete the connection file if LW has not been used for 30 days or longer.

If still connection problems after that, then it might be related to any firewall you have, or your router's NAT in which case port forwarding might be needed.

By the way, does the Linux LPE open ok in Java 7?