env_projectedtexture is a fickle mistress
Does anyone know of a reason why an env_projectedtexture wouldn't obey it's TurnOn input? I was having problems in a Portal 2 map with multiple env_projectedtextures even though I was only turning one of them on at a time. Then I started noticing that the texture from the standard observation room sometimes wasn't coming on when you start the map.
So as a sanity check I built a room that only has an observation room (altered so that you can turn the lights off) and a floor button to control the lights. Sure enough, sometimes when I step on the button to turn the lights on, the env_projectedtexture doesn't activate. If I turn on 'developer 2' in the console it shows the TurnOn input being fired, but nothing happens.
Sometimes you get streaks where it works 5 or more times in a row, and then again sometimes you get multiple failures in a row.
I'm stumped. I don't know if it's a bug in the engine, a bug in Portal 2, or if I'm just missing something incredibly obvious. (I know which one is most likely.) 
Post your .VMF so we can takea look into it.
useful tools and stuff here on TWP 
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Yes, I agree with jose - upload the .vmf
My guess is that there's a mistake in the settings or something, but also try killing yourself/reloading the map. I've had trouble with it not working, then I've reloaded the map and it's worked fine.
OK, I figured it out. The PeTI observation rooms set the "Appearance" of their env_projectedtextures to "fluorescent flicker". Apparently, this doesn't work. But I guess whatever internal timer is supposed to change the brightness of the light keeps running in the background, and the texture gets set to whatever state the flicker is at the moment you turn it on. So if you activate the texture during the dark part of the flicker you don't get anything.
I set the appearance to Normal (which has no variation) and now it works every time.