My first suggestion would be to disconnect your Slingbox from the bridge and try with a different device, maybe your computer. Conversely, try plugging your Slingbox into the router directly. You need to isolate where along the network path the problem is happening. I suspect it's the bridge (or more properly, the bridge configuation). This will confirm that.
I've seen a number of cases where wireless bridges fail until you go into their configuration and specifically tell them which wireless network to join. This is especially true if the wireless network has security enabled.
If you test connecting the Slingbox to the router, you can skip hooking up any video sources. It should show up on the network and you can connect to it even if there's no cable, DVR, etc. attached.
Try these things, post back and say how it goes. If you notice any other clues or details, those would be helpful too. If you're still stuck, we can dig a little deeper.
Good luck !