Thank you for the speedy response. I ended up downloading and installing the QuickBooks Desktop Pro 2012 Trial and upgrading all my companies to that version from the 2009 version. I then proceeded to install the QuickBooks Desktop Pro 2015 Trial and again converted and upgraded all of the files. Finally, I went back into my 2019 version and had no issues upgrading the company files to the latest version. It took an awful long time (approximately 8 hours) to perform the upgrades in this manner, but I was able to get it done and ultimately made my customer happy! Lesson learned here:  Do not let the software get too far out of date!  :)