I accidentally discovered this while sending a large (3MB or so) text document to a friend. I connected and pasted the text in as usual, then hit send and the little progress bar at the bottom came up. So I then went to a different window and did some other things, and having a habit of closing inactive (or so I think) AIM windows, I, without even thinking, closed the window that was sending the text. Well it turns out that when I closed the window I succeeded in locking up my friend's Win98 box. Out of curiousity, I tried the same thing on my own win98 box, and it worked. The same thing happens on XP also, but it is more likely that you can recover. So it appears AIM is not the most stable application while files are being sent/recieved. It only seemed to work for me with text, but I only tried mp3 and avi as the other format.