Have a look at the image below

I've somehow messed up the scale, causing all the keyframes to squash down horizontally. This makes it tricky to select them

Any idea what I've done, and how to put it back to normal ?

It looks like you've lost the scrollbars that make it possible to expand the scale
both horizontally and vertically.  If this is permanent (not just on one PZ3) you
might try a "partial reinstall".   In other words, re-run the installer for the last
Service Release, which should overwrite most of the underlying DLL files.

Nope, it's not permanant. Restarting poser fixed it, even on the same file.

But any idea what could have caused it? i was messing around with layers, and the frame count of the animation.

Well, that's good. 

"Messing around with layers" is a good hypothesis for the cause of the problem. 
The whole Layers system is totally screwed, and I'm not at all surprised that it
screws up the other parts of the animation code!

The whole layers system is screwed? That's a glowing endorsement of the product..

I did ask about it here once, and nobody seemed to have any clue how it works. So I've been sort of blundering my way through it, getting some limited sucess and confusing results

"limited success and confusing results"

Yup, that's the same thing I got from the Layers!

If Ockham can't get the layers working properly, then what chance do the rest of us have? 

AH   Les and Ockham located in the same place at the same time -
hey guys do you have a good way to copy and paste animation curves in the animation graphs windows? I BELIEVE  if you position and click your mouse and drag just right...Poser will function to highlight  whatever portion of your curve and let you copy - but it is impossible to really get the work done exactly and efficiently , and also when you paste, it is pretty hard to get the paste to go down in the right spot, if the graph you are pasting to has any activity already in it..... If there was a way to copy the whole animation graph of one body part, and then paste this whole animation curve to a different body part's graph......... and better yet, also be able to paste the INVERSE curve, that would rock. Hmmmm, I wonder if I am asking for one of the functions that you might already be performing inside your JIGGLES,  Ockham.