Just downloaded a 2017 tax data file from the TurboTax website without error.
Clear cache and cookies on your web browser. Close the browser and re-open.
To access your current or prior year online tax returns sign onto the TurboTax website with the userID you used to create the account - https://myturbotax.intuit.com/
Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on the Year and Click on Download .tax file or Download/print return (PDF)
If the problem persists, change your web browser.