One of my usual stopping spots for news on all things sci-fi and fantasy is io9, and pretty much every day there's multiple things worth checking out. Today there's a rather nice one on the Ten Types of Writers' Block.
I have to admit, #2 (Plenty of ideas, but nothing sticks) and #4 (stuck in the middle with nowhere to go) were frequent problems I had. Those two comprise a key reason why I have a handful of started novels buried away in my files. I would have a concept for a book, and jump in a start writing... and then find it doesn't go anywhere. A few of those was what helped me accept that I'm an outliner at heart.
Now that I am an outliner, of course, I do hit bumps with #3 (stuck between points in the outline). I've often had those moments where the path from A to B to C just isn't as clear as it seems it out to be. Often what I've done is just go ahead and write C and leave a notation for B to write later. Usually what I've found is that the problem was I had to do a lot more things than I expected to get from A to C.
My main paralyzers at this stage are numbers 7, 8 and 9-- all of which boil down to that inner voice of self-criticism. I'm often staring at the screen thinking, "This doesn't work, this CAN'T work, I'm a hack and everyone will think this is stupid." Then I get over it, best I can, and plow on through.
What else am I going to do? Not write? Yeah, that doesn't work either.