Well my guess is then that your speedstream is blocking ports. As far as I can ascertain, this modem only utilises UPnP whilst used in USB mode. Thus I suspect you'll need to do port forwarding. There's 3 steps with the 1st (static ip) probably the most important or else the port forwarding won't work.

The Steps:

1. Set up a Static ip (see instructions under step 2 (4rth link listed on that page!)

2. Forward port 6346; Port forwarding instructions for Speedstream 5200 which also includes instructions for setting up a static ip. Choose Limewire from the list when you reach the port forwarding stage.

3. Within LW: Manual port forward instructions & sample image & 2 posts after that.

A & B & C