Hi, i have this problem, I can't fly or use skills. I play in survival mode, but when i press double space or the V nothing happens. As a detail, I use mods apart from the normal minecraft mobs, like the mo'creatures mod and the elemental creeper mod. In the case of mo'creatures, I have become a bee and a bird, with neither I could fly.
(english isn't my first/native language, sorry for mistakes or misunderstandings)

I await answers, greetings.