I've been writing professionally for 26+ years, and I've never had writer's block. I believe it exists; it just hasn't dropped in for a visit with me yet. I hope it never does.
There are times, though, in every book where I cannot make forward progress no matter how hard I try. It's as if the characters have just shut up, folded their arms over their chests and turned their backs to me. I write, delete, write, delete, walk, fuss, bang my head on the desk . . . then remember: the fact that the story won't move means that I've gone wrong somewhere. This was something I experienced in the first book I sold on a partial, so you'd think all these years later, I would remember it, maybe even expect it, and immediately know what to do about it.
The solution is simple: I go back thirty or forty pages and start reading, and when I see that the story's gone off on a tangent, that's where I start rewriting.
But I can't just say, "Oh, okay, this scene isn't working so I need to flip back a few chapters." It's like I have to go through the writing/deleting/writing/deleting/head-banging. It's all part of the process.
Since I'm fortunate enough to have a process that I actually (at least partly) understand, couldn't it be a simpler one?