Creating PDF Hangs at Post Processing

Frame 2019, Fully Patched (No updates available), Unstructured. We have created a multi-level book that has a main book that contains multiple books (chapters) using folders. When using the Save As PDF option, the processing hangs at the postprocessing step and will not complete. I left it running overnight just to make sure I wasn't being impatient. I have tried printing to postscript and distilling. This doesn't work because there are foldout pages in a couple of chapters.

I read in this forum that bad art can cause this so I started paring the book down to try to locate it, deleting first some files, then entire sub-books incrementally. I now have it down to the main book with a few front matter files (no art) and one empty sub-book and am getting the same results.

The error in the log file says: [1104/100835.980:ERROR:registration_protocol_win.cc(131)] TransactNamedPipe: The pipe has been ended. (0x6D)

I was able to publish the sub-books individually but not at the main book level. I was able to create a PDF at the main book level a couple of weeks ago.

Am I missing something obvious? The information in the help files is pretty scarce and generic. I'm also not able to find much information on books-in-books.

I've been using Frame for many years (mostly structured) but this sure has me stumped.

Any pointers would be greatly appreciated.