Hi Arno,
You may be experiencing some program-related issues.
With that, let's perform the verify and rebuild steps to fix the issue when converting to QuickBooks Online. To get started, close all windows. Then, from the File menu, select Utilities, and then Verify Data.
If you see an error message—search for it on our QuickBooks Desktop support site for how to fix it. If the system prompts you with, Your data has lost integrity error, you'll have to rebuild the program.
Furthermore, visit these resources to get more ideas about managing invoices, payments, and customers:
I'm always around whenever you have concerns.
