i have a few questions... is your laptop connected via Wlan or ethernet with that secondr router?
and can you access internet with your Laptop ?
Laptop needs to connect to sling server to be able to find your slingbox IP address (external and Internal as they are both saved on slingbox server). After your laptop gets those two adresses... it will first try your local IP, and then external, and after that it will use some relay network.
you should open and forward all trafic on port 5201 to your slingbox IP on your first router, and then forward all traffic on port 5201 from your second router to your first router. If your laptop is connected via cable to your router you should consider replacing your second router with a simple switch.
either way, Internet connection is a must.