Thanks for joining this conversation, @AmCh.
First and foremost, I appreciate you following the troubleshooting steps provided by my colleague above. Allow me to step in and share some insights about how to accountant copy's work in QuickBooks Desktop (QBDT) Premier.
A possible reason you're getting this error is that you and your accountant might have different versions of QBDT. If that's the case, make sure that the gap is at least one year. Additionally, when opening an Accountant's Copy in a newer version of QB, the file should be upgraded. Any changes you make can be incorporated if they were made using a compatible version.
For more information, check out this article and scroll down to Product versions: Accountant's Copy and QuickBooks Desktop: Use the Accountant's Copy.
As mentioned, the steps to fix this may differ depending on the type of error you're getting. Please refer to these articles for more troubleshooting steps:
That should get you fixed right. Please reach out in the comments to let me know how it goes or if you need anything else. I'll be happy to help. Have a wonderful rest of the day.