I got the same error. I saved to a different folder and it worked. Cause was "Controlled Folder Access" on Windows 10 blocks programs from saving to your My Documents folder unless explicitly permitted. Thus look for a notification in system tray for a notification it was blocked. Open the notification and go through the steps to allow it. From thereon it TurboTax.exe will save to the My Documents folder.
If you don't see or can't find the notification, simply click on Start button, Settings and in the Find A Setting box type in "Controlled Folder Access" (without the quote marks)
