I had this bug in previous versions. Files in my download queue would instantly jump to 100% (without really downloading anything) and the 'Could not move to library' message would appear. This error would happen with every subsequently selected file but , as you said, restarting Limewire solved the problem. In my case, the problem didn't appear to be related to illegal characters.

Funnily enough , I haven't yet encountered this bug LW2.5.5