It's my guess it's due to this: License requirement (click on link)
If not that, then it might be the Java, so I'd uninstall all java versions, reinstall using only the OFFLINE version: Download Java software from Sun Microsystems

Other than that, the LW preferences may need refreshing. Make a note of all your options settings, including your download location, then try deleting your LW Preferences folder whilst LW is closed; instructions here: Point #2 & 3 in Fixes for Limewire (sample image included at bottom of page.)