Well i've been trying to figure this one for a while now with no luck. I've googled with no luck as well, I even attempted to use Bing...which was also no use.
The problem: It seems windows 7 heavily dislikes multiple connections while downloading. It doesn't seem to mind when one thing is downloading but you get multiple connections going and it freezes right up.
I've had freezes using bittorrent downloading multiple items at once. I currently have one downloading and it's doing fine.
In limewire it froze up when about 5 songs were downloading.
In firefox it froze while opening multiple tabs at once.