If a download remains in requery mode very long (two days or longer) you can do three things - search for that file manually again (that helps at times), restart LimeWire (at times, if you have been online very long, even that might help) or kill the download (after two or three days you will probably have to accept that you won't find the file).

If the download goes into requery mode directly after trying to download it, - kill the download at once, the host is either not accessible or it doesn't share the file anymore.