There is such a thing as Creativity Gridlock. This is a different beast than Writers' Block. I've had Writers' Block, where you just STARE at the blank screen until your head bleeds because you KNOW you should KNOW what to put there, but you can't think of what. Now, I should point out that that is different form just not having anything to write. Then you don't even open the screen. With Writers' Block you feel this nagging something that you should be writing, but don't quite have it. It's like that feeling of trying to remember that kid in third grade who did that thing with his glasses... you know you KNOW it, but you can't quite get it.
Creativity Gridlock is when you do know. You know what to write for a few pieces. You know the whole bit that will come up in the end. You know this other cool bit in the middle. You know how four other stories are going to go. And ALL THAT STUFF wants to get out your fingers, and what you can't figure out is what to write FIRST. And NONE of it is willing to shut up and wait their turn, all those stories want out NOW, and you can't write any of them.
At least, I have moments like that, and I don't consider it Writers' Block.