Is it a yellow Werner break down?  I had one (can't remember the model name) and they ended up doing a return\recall on it because the model proved to be very difficult to separate.

Had the same problem a couple of times with a different make/model. The problem seemed to result from water causing the composite shaft material to swell slightly, and  getting some river-grit in the junction between the blade and the shaft didn't help either.

The first time it happened I took a heatgun (hairdryer is fine too) and heated up the shaft at the junction with the blade. This will expand the diameter of the shaft ever so slightly, and do so before the bit of the paddle on the inside of the shaft expands to an equal degree. This was enough to allow me to pull if apart the first time.

The second time this happened, it was more stubborn, so I shot WD-40 or something similar into the juction, then heated the shaft, then yanked the paddle as hard as I could through a padded constriction (wrapped towels around the uprights on a weight bench) that was tight enough to catch the blade and that worked after 2-3 tries.

Since this was a cheapo-paddle (aquabound) I decided that I never wanted to deal with that kind of hassle again so I sanded down the junctions on the paddle-ends ever so slightly and I haven't had the issue since. Not sure if anyone would want to do this with a nicer Werner paddle,but it's an option (though it might void the warranty?).

Great suggestions, thanks. I used it for about ten days on the Grand Canyon and that is some fine sticky dirt. I'll let you all know what eventually worked.

Always a good idea to store your multiple piece break-down broken down when not in use.  If you leave it together between uses, it's more likely to freeze up.    

If it happens again penetrating oil might work better than WD40, or at least not take as much.

Kyle