I too had difficulties after downloading sp2. To fix the problem on my machine I did the following.
1 -Go to start, control panel, windows firewall.
Click on the exceptions tab at the top. If limewire is not listed, click add and point to it.
2 - Go to start, control panel, windows firewall.
Click the advanced tab, highlight local area connection, click settings
Click add, in description type “gnutella” in name type “your computer name or IP address” and in the external port put your port number. Click add
3 - Follow directions from number 2 again but before clicking add make sure the “UDP” is selected.
4 –go to control panel, internet options
click connections, click LAN settings. Automatically detect settings should be checked.

If you have another firewall running make sure that sp2 is working well with it and that limewire is also added there. There are issues that seem to stem from the 2 firewalls working together. You might want to try turning off any other firewalls to see if that works sp2 does not seem to play nice with others.

This is all it took to get mine working fine again.