Has your Evo been updated to version 3.30.651.3? If not check for updates, because Sprint has just released an OTA update that is supposed to fix some camera issues that is making 3rd party video chat apps like Qik and Tango not work properly.
Sprint says that only new buyers of Evo that have version 3.30.651.2 should have this problem. Customers with an older version shouldn't have the problem, although there are reports saying that even though they had an older versions, they are still getting this update. Perhaps it's best if you don't install it until Sprint makes this more clear.