This happened to me after I installed SP3 from Microsoft last week and after "Lord of the Rings" suggested I replace the Gnutella.net file in "User name\App data\Roaming\Limewire" everything worked properly.
You can get a new copy of gnutella.net by following the forum, "Technical Support", "Connection problems",from the beginning when you first start to look into all these forums. In there you should see, "If Limewire will not connnect",then look for, "delete/replace Gnutella.net file" and follow the instructions to download a new copy. (To get the "Apps Data" folder to appear you will have to go into the "Control Panel" and select the "Folder Options" section, and in the view section of that go to the section where it says "show hidden files and folders"). After this you should be able to go back into "User name\App data\Roaming\Limewire" (as shown above) and you should see Gnutella.net and be able to cut and replace the old one with the one you have downloaded into where it belongs.
Good luck!