I have Slingbox Solo set at home and everything works fine in my PC (App, IE, Firefox, Facebook), Symbian phone and iPad.
Only in Lumia 900 WP remote control does not work (Video streaming works fine).
You are not alone out there.
I have a Lumia 800 with exactly the same problem.
This might seem obvious, but those symptoms mean that the fault lies with the 900 app so don't bother trying to do anything with the Slingbox (power toggle, reset, re-run setup...), it won't help.
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