Two router setup?
Why the two router setup? UPnP may not be working or not enabled in the router(s).
Did you setup port forwarding? Port 5001 I believe, forward it to the ip addy of your slingbox which by default is 192.168.1.237. If you setup port forwarding, then UPnP will not be needed.
I just got my Schwingbox last weekend and I *LOVE* it. Its awesome over my WAN, great over the internet, and can somtimes even watch passable video over the EDGE network. Sadly, 3G is nowhere near my area.
It really surprised me how well the slingbox does, even with all the probs the Kaiser has with video. BTW, slingbox is aware of the HTC video probs but so far has not even tried to improve or refine their code ala Coreplayer.
Also, you do not need to a registration key to use the software, it is free to try for 30 days. Also make sure you downloaded the correct version of Slingplayer Mobile. There are two versions, one for smartphones and one for Windows Mobile 6.
HTC Kaiser <--- the daily driver
L26 Diamond V9 ROM 3.55.502.1
ROM Date: 06/25/08
ATT Tilt (8925 Kaiser 100) <---just for playing with.
Between ROMS at the moment