This can happen if your QuickBooks Desktop application is running inside a Parallels Virtual Machine while your data file is stored natively on Mac. This forces the software to access the file over a virtual network.

Please note that 2020 is already an unsupported version of QuickBooks. Because of that, it is increasingly prone to these types of environment-driven technical glitches. You'll want to upgrade to the latest version to avoid interruptions and similar issues. 

To check if this is a data file corruption or a Parallels configuration or pathway issue, test it entirely within the Windows ecosystem. Here's how:

1. Open the Mac Finder and locate your QuickBooks company file (.QBW).
2. Copy the file, then paste it directly onto the Windows 11 desktop (inside the VM environment, ensuring it's on the local C: drive).
3. Open QuickBooks inside the Virtual Machine.
4. Go to File, choose Open or Restore Company, and then select the copy from your Windows desktop.
5. Create the backup now.

If the backup succeeds, your data file is completely healthy. The error is purely caused by the program reacting to the file being hosted on the Mac file system over the Parallels network.

To bypass this, create a portable company file instead of a full backup. Then, restore it to overwrite or rename the file back into your Mac folder.

Let me know if you have other questions. We're always here to help.

@gerdgoebel 

Install the trial version of QB Desktop 2020 Enterprise or QB Desktop 2021 Pro to isolate the problem.

First of all, I have this running on my Mac for years without any problems. And since yesterday there were no Mac OS nor W11 updates. On the Mac I am on Tahoe 26.5, on Windows I am on 25H2 with latest security patches.

Yesterday, I imported our daily sales transactions, did the backup with Quicker Verification, then the backup completed without any errors, and I closed QB.

I have several backups of the QB database on external SSD. 

I copied yesterday's database to the Windows desktop, opened it, started the backup with quicker verification, but get the same error here as well. 

This is now on the old VM that I have used yesterday and the days before.

I get the same error as before. Then I restored a QB backup from last week, did immediately a new backup with quick verification and did NOT get the error.

Just now I restored the QB database from yesterday to the Mac folder I always use (on the new VM), the restore went find, and an immediate backup with quick verification was done without any errors.

At the moment I have no idea why I got this error, thinking about it had something to do with the new VM, or with me not logging onto my QB account, but QB is at least running again.

I now do yesterday's sales transactions from our store again (like I did this morning), then see if the new backup works correctly.

I just imported yesterday's sales transactions, did a backup and it finished without any problems.

The only thing different on the new VM was the Saasant Importer. I had downloaded the latest version, it sure worked correctly doing my various imports, but then I got the error I posted.

I have replaced the Saasant Importer with the previous version (the one I had on the old VM), and todays imports were done with the older importer.

I don't want to speculate, as the Saasant importer is a very reliable app and I have used it for many years. If it would have anything to do with the error, then I should not have gotten the error after copying yesterdays database from my external SSD back (just with copy/paste, which I have done often as well).