Problems with generating PDF with video from FrameMaker

I have a book (about 300 pages; created with FrameMaker 12 exported to PDF using the Save as PDF function that includes about 30 video tutorials (all mp4s). So far, I have not been able to successfully generate this book and have the tutorials work. The pdf generates but will not open and Acrobat throws up a message "There was an error opening this document. The root object is missing or invalid." Is there a limit to the number or overall size of the document with video in Acrobat? I have successfully used the FM12/Acrobat DC apps to generate technical manuals with video (also MP4s) many times in the past. Now, for some unknown reason it's not working. Help!