So, it appears this program has a problem opening database files after a certain modified date for reporting. To get around this issue, with the program closed, i set the year on my PC to 2014. I then opened up the proventure invoice file, went to reports and was able to display my invoice report data. Now the reports will only display the data up to 2014. So, I chose the Product List report, which generated the error, switched my year back to 2020 and selected the invoice report again. I was now able to print the report for the year 2019.
I believe this stems from an issue with the modified date of the database files and how the program uses the date. Now this worked for Invoice Report, the others I haven't tried. But my guess is if you change the modified date on the other database files using a program like "Attribute Changer" while your PC year is set to 2014, they will probably work.