Error 1635: This update package could not be opened...
This error occurs when installing TurboTax. The full message reads:
Error 1635: This update package could not be opened. Verify that this update package exists and that you can access it or contact the application vendor to verify that this is a valid Windows installer update package.
This problem occurs when a prior TurboTax installation did not finish installing or uninstalling, leaving it in a broken state. The residual files on your computer are detected by the TurboTax installer, resulting in the message.
The first solution you should try, if you haven't already, is uninstalling TurboTax and then reinstalling it again.
If that fails, you can forcefully uninstall and reinstall TurboTax.