Hi westwater, 

Thanks for joining this thread and letting us know about your concern with exporting report to Excel.

Generally, the Excel cannot open the data file error message can be resolved by restarting the computer. However, if the error still persists, the steps given by my colleague @FritzF can do the tricks. 

Since none of the above steps fix it, I'd recommend giving us a quick call. Our support specialists can securely access your account and double-check what's causing this to happen. 

They have the necessary tools, such as a screen sharing session to help determine which additional troubleshooting steps to do specifically to your account. Here's how to reach us:

1. Go to this link: https://help.quickbooks.intuit.com/en_US/contact.
2. If you're prompted to choose a product, choose QuickBooks Desktop.
3. Pick your QuickBooks Desktop version.
4. Choose Solving Issues & Error Messages, then File & Network Management.
5. Scroll down to the Here's how to connect with a QuickBooks expert page.
6. Click the Get Phone number button.

You should now be able to export your reports to excel again in no time. 

Please update me as to how things go. Rest assured, I'll still be here to help you out!