Writer's block is my subconscious's way of telling me I'm about to screw up in a big way. I can write mediocre stuff, no problem. But if I try to force my characters to move out of character, ZZZT.
As soon as I give up on whatever I'd planned, I'm fine. I don't even have to know what I'm going to write next, as long as it isn't Just Plain Wrong.
...Nevertheless, I don't want to hear any characters bitching about not getting any. I'm just saying. "So...I was going to make you lovers..." "No, no, that's no good; we're going to be not lovers." "Okay, got it."