Is this using P2P?
As Paul said above, if you max out your connection (especially the upstream) you can cause it to drop.
Try & cap your upload & download in your P2P/whatever software.
Have a look at this:
http://homepage.ntlworld.com/robin.d...mtips/p2p.html
Maybe could also be that the modem simply can't handle the level of traffic it's seeing from your usage.