Thanks for getting back in here, @JanEG. Let me guide you the way on how to fix this. 

You're right, right now our option is to contact our support team. They have advance tools to open and check your account. By doing this, they can also further investigate your file and provide the necessary fix to resolve this. 

You may consider following the steps given by my colleague, @MaryLandT to reach our team. 

For additional information, I suggest opening this resource:  QuickBooks for Mac file to QuickBooks for Windows.

Let me know how it goes. I want to make sure everything is taken care of. Have a good weekend.