IDCS6 not exporting a pdf.

Your post is unclear, Is it just this one 450 page book you are having issues with., or other documents as well? If the latter, try make a new sample document (even one page) and see if that exports, properly. If it doesn’t, there is something wrong with your install, so the troubleshooting others have suggested (to purge preferences, etc) is the first route for you.

If it’s just that one book, try export small sections of it at a time. If any are successful, then there is “something” in the file that’s causing you issues. Keep doing sections until you narrow it down to the problematic page.

As a test, try print to Postscript the document and use Distiller. This is not a recommended approach normally, but might help determine where the fault lies, as Distiller might indicate which page is causing the issue if/when it fails.

If you are still having issues, maybe you can share a file for one of us to check. If it’s sensitive, you can DM one of us (I’m available)

-Brad

Jaal, here is some comprehensive troubleshooting.

What OS are you working with?

The problem might be only one page or one object on one page. Export is 100-page chunks to find which 100-page range has the problem, then export that section in pieces, eventually finding the problem page. Export just that page with different objects removed to find the problem item. 

InDesign, including CS6, processes PDFs in the background. It might be overwhelming your system. 
Output the file in sections and combine the PDFs in Acrobat. Another option is to disable the background processing.

Hi ​@jaal , Did you try the regular troubleshooting—delete Caches, of that doesn’t work delete preferences?

What happens when you try? What operating system?

I’m sure you’re aware that CS6 is closing in 15 years old and there have been more versions released after than there were before so you’ll need to keep your expectations low and provide a lot more information.