Let's try doing a clean install and delete all the cache of the program. Make sure that you have the backup data folder before start doing this.
Uninstall your software first, then go to the folder location below on your computer then delete the Express Invoice folders:
C:\ProgramData\NCH Software
C:\Users\(Your computer profile)\AppData\Roaming\NCH Software\[Express Invoice](%3C___base_url___%3E/forum/37-express-invoice/)
If you can't find the AppData folder, set Windows to show hidden files and folders with the steps from this link: https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files.
After deleting the Express Invoice folder, restart your computer then install it again from the next link http://www.oldversiondownload.com/oldversions/expressinvoice-7-25-2019-11-13.exe
That should do it. Please try it again after that and see if that fixes the issue.