Adobe Illustrator ver 27.3 - Unknown error message when trying to save any ai file as a pdf file

I had been able to save ai files as PDF files (save as) - no problem. However it now occurs that any ai file that I try to save as a PDF file generates an errror message:

An unknown error is detected. To help us investigate -- .

Given this problem is not specific to one specific file don't know that sending a file would be helpful

Have tried resetting preferences.

Reset the Settings folder by renaming it.

Coworkers are able to open same illustrator files and save as PDF with no error message.

Using Illustrator on a PC.