It's because the file isn't available at the moment, for any of a number of different reasons. But LimeWire will continue searching for it, in the event it does show up (subject to some problems noted all over this board). As far as why you have to wait 285 seconds, I would guess that its because if the file isn't available right this second, it's most lkely not going to be available in 5 seconds - so there is no sense in congesting the network with hundreds of thousands (total, from everyone) of requests every five seconds. Every five minutes or so should be sufficient.