Cannot save PDF

Unfortunately it could be anything. Months ago I was working on a server that had permissions issues and this would randomly happen when I was exporting PDFs, and it was infuriating. After several attempts it would work, nothing changed in the file and it would work.

If that's not what's happening in your situation, there may be a corrupt graphic or something the PDF engine just doesn't like. Unfortunately it is a bit of trial and error to fix but it is a case of seeing if the first half of the document exports; if it does, try the second half. If it does, great - merge the two files in Acrobat. If not, take the section that doesn't export and split that into two to see if either half of this section exports... and so on until you can narrow the issues down to a page. From there, take items off of the page until the page exports and then you will know what is causing the issue. The next problem is fixing that issue... but have to know what is causing it first using this method of locating the problem.