I know it's been a long time since the OP asked about his problem, but I'm getting the same problem and same message.
When I click NEXT I get a screen with the settings for the Manual Router Setup. The IP addresses look fine and the Port is indicated as 5001.
I went through the port forwarding process on the ATT U-Verse (Uverse) 2WIRE 3600HGV.
But I still get stuck in the endless loop.
BTW, on the TV connected to my SlingCatcher the message I get "unable to connect to the Slingox due to a network error".
Internet viewing works fine on my Mac.
What do I need to do to have my Slingcatcher error resolved?