We recommend you to run the Setup Assistant for Internet Viewing one more time but using the Manual Setup process.
Just make sure to enable both of the protocols (UDP and TCP) when creating the rule for Internet Viewing.
I also have this issue, however I have tried the following with the noted results.
I have firmware 2.1.90 installed on my SlingBox Pro-HD
When I run the Slingplayer (Ver 126.96.36.1992) on my computer it works correctly.
When I run the Slingplayer (Ver 2.1) on my iPhone 4 it works as long as I have WIFI enabled and I am connected to the same network that theSlingbox is connected.
After I do a reset on my SlingBox (hold the reset button in for 15+ seconds), the following occurs:
The Slingplayer on my iPhone now works over 3G or outside my home network,
However, when I run the SlingPlayer on my computer, the video pauses and stops and starts and many frames are dropped. The video is essentialy not usable.
I then drop back to SlingBox Firmware Ver 1.4.060, which works correctly, also with my iPhone, but not in HG. I then upgrade the Slingbox back to 2.1.90 and all works correctly except my Slingbox on my iPhone will not connect on a 3G network or on a network other than my home network.
The bottom line is firmware 2.1.90 does not work very well. If you browse this forum you will see that it has many problems for user.
How about and update SLINGMEDIA???