Your router probably has only one port forwarding rule setup for one Slingbox. Since you have two Slingboxes, you will need two seperate port forwarding rules. Each Slingbox will also need to be configured with its own unique port. The stand port used by the Slingbox is 5001, so you can set up the other Slingbox as port 5002. Then you will need to another unique port forwarding rule for the other Slingbox.