The only Situation where I would get this particular error is, when I try to download MP3s from a bearshare user.

Problem in extenso:

Bearshare (and another Gnutella Servanct whose name eludes me at the moment) started to add additional information to search replies. So if you search for a music file most servants will basically reply just "Yeah, I have that file, it's this and that size", while Bearshare will also reply "...and its having this bitrate and whatever stuff I know about the file in question".

Xolox doesn't handle this elongated message very well, which leads to the effect that only the first file from that one Bearshare user will be displayed okay, but all other files he replies with will have lost their first character ("Britney Spears.mp3" will become "ritney Spears.mp3") and will display a size of the gigabyte range. Xolox simple misinterprets the answer.

Now when you still try to download these files it causes some kind of error in xolox (probably an overflow of some kind, but thats just an assumption) which will display your error box.

Solution: either make sure that the file is not one of the corrupted ones or get a second gnutella servant just for mp3s.