OK, let's try and find the problem...

In your new 600 frame animation, let's have a look at a few parameters.

I assume you have a figure or two in your animation, select a figure, select hip, look at the graph of the transform of, say, x.

There will probably some kind of squiggly line with some dots on it. The dots are your keyframes.

How many keyframes are there? Is there one on every frame, or one on every second frame, or less?

If there is one on every frame, and the value for frames 1 and 2 are the same, and 3 and 4 are the same etc. (which is what you are implying by saying you have pairs of frames that are the same) then there is something you can do...

Go to http://ockhamsbungalow.com/Python/ and download "Sparsifier" and "Periodizer" (and anything else that you think might come in useful!).

These are python scripts and very easy to use, and very likely to sort your problem.

If you know how to run a python script, just make a backup of your existing file, check out the readmes and give it a whirl.

If you don't know how to do this, have a quick peek in the manual, it's easy enough!

I find ockham's scripts so incredibly useful that I put them in a folder of their own somewhere like: Poser Pro 2012RuntimePythonPoserScriptsScriptsMenuOckham (or something like that - I'm quoting from memory), that way I can easily call them anytime from the scripts menu in Poser.

Good luck!