Hi Jan13,
I know how important it is to be able to back up your company file so you can save your data for future reference. QuickBooks Desktop gives you the flexibility to back up your file manually or automatically. I'll be happy to guide you through this.
A good starting point would be to ensure there's no company file issue causing this warning message. Like @Fiat, I'd also recommend running the tool hub to resolve any potential bugs in your file. Here's how: Fix common problems and errors with the QuickBooks Desktop Tool Hub
To make sure you're following the correct steps for your back up, and for more details in this procedure, check out this useful article: Back up your QuickBooks Desktop company file
I hope this helps you get back on track! Don't hesitate to reach out if you have more questions.
