Hi there Dean46,
It's vital that you be able to access your file in order to be able to manage your books. QuickBooks Desktop is a great program able to help you manage your books so that your financials can be up to date. I can point you in the right direction for assistance with this error message.
For help with resolving this error message, I recommend reaching out to the QuickBooks Desktop support team outside of the Community. They'll be able to provide further troubleshooting in order to help you get back into your file to manage your books. You can reach out to them using the steps provided in the QuickBooks Desktop software support policies.
If you have any other questions, feel free to reach out here.