Completed downloads disappear

Hi,
I have Mac OS X.2 and Limewire 2.5.5.
About half the files I try to download disappear. In the Search window, it claims to be completed, but in the Library window, I can't find the download in either the Incomplete or Shared folder. Sometimes a download will be in the Incomplete folder while it is downloading and will disappear (and not reappear in the Shared folder) when it is complete. I have searched my hard drive but can't find the disappearing files. I've checked the location of the save folder and that doesn't seem to be the problem. I'm not getting the "cannot save to library" message that other people have written about. iTunes is set as my default mp3 player and, when Limewire works (about 50% of the time), there is not a problem launching the music in iTunes.
I'm new to Mac and to Limewire, so any help would be appreciated.