From the FAQ:

Q: Why does LimeWire sometimes stop downloading the file I requested and display 'Requery Sent' in the status column?

A: The files available on the Gnutella network reside on the computers of users that choose to share them. If the user sharing a file you are downloading disconnects from the network or becomes unavailable, your download will fail. If a download fails to complete, LimeWire will automatically attempt to find an identical file that is still available on the network and resume you download. While searching for identical files, LimeWire displays the status 'Requery Sent.' If this message is displayed it is likely that LimeWire will not be able to resume your download and it is recommended that you perform a new search and download a similar file.