I'm not even sure if I put it in the right category, but... Let's try it. I'm following this tutorial: http://www.photoshoplady.com/tutorial/apply-3d-effect-on-movie-poster/3654
When I get to the time where I need to go on Image>Adjustments>Channel Mixer I can't click on "Channel Mixer". It's not clickable! I don't know why. I have no idea of what I am doing now. Can someone help me, please?