This problem has been bugging me all day and I sense there's a really simple solution.
When trying to render my game's depth map I get the following error:
XNA Framework HiDef profile does not support alpha blending or ColorWriteChannels when using rendertarget format Single.
I've tried setting BlendState to Opaque and even setting ColorWriteChannels to None. Doesn't fix it.
This is all in my game which is based on the game state manager sample for xna: http://xbox.create.msdn.com/en-US/education/catalog/sample/game_state_management
If I run the exact same code in a completely blank project with the exact same model, it works just fine! So I assume the game state manager is changing some settings that are causing it to fail? What else is there that could be causing this? It's driving me insane.