If updating the driver doesn't work, what's the next troubleshooting step for Error 709?

Roll back the driver to a previous version. In Device Manager, right-click the printer, select 'Properties,' go to the 'Driver' tab, and click 'Roll Back Driver' (if available). Also, check for Windows Updates – sometimes, Microsoft provides driver updates through Windows Update. Consider performing a System Restore to a point before the error started occurring.