Problem with frames

I've been having problems to make gifs in PS CS5. Whenever I want to make frames from layers, I can't even choose the option -the programme doesn't allow me to do so. Is there anything I have to do after opening the gif file so I can use the "make frames from layers" option?

Sorry for the silly question, but I'm getting on my nerves with it *lol*. Anyway, thanks in advance :)