If you want LimeWire to find new sources you have to do another search for the file you are downloading manually. If LimeWire doesn't restart the download after the search results arrived kill it (unless it's a big file and already halfway downloaded - in that case I would retry later).

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Morgens ess ich Cornflakes und abends ess ich Brot
Und wenn ich lang genug gelebt hab, dann sterb ich und bin tot

--Fischmob