I've also seen this happen in LimeWire myself and when it happens and you kill the download and try to redownload it, LimeWire then claims that you are already downloading it, even though nothing is listed in your download list. This was in linux with java 1.4.2_03 but I don't remember which LimeWire I had installed at the time that had that problem. The only method that succeeded in getting it to resume the frozen download after killing it was exiting limewire completely then reloading it then searching for the same file again and redownloading it.