This error can be caused by issues with QuickTime. Follow the instructions below for resolving this problem:1) If Pro Tools LE 5.3.1 does not find QuickTime during initial installation, it will automatically take you to the Install Wizard. Allow the Pro Tools LE installer to continue and install QuickTime. Assuming it is successful, you will receive a Pro Tools LE 5.3.1 install completion message.2) Restart the computer.3) Before launching Pro Tools, open the Add/Remove Programs Control Panel and uninstall QuickTime. There will be 2 options, "Uninstall everything" or 'Uninstall." Choose "Uninstall everything." This will remove all software relating to QuickTime.4) After successful uninstall of QuickTime, launch Pro Tools LE 5.3.1. you should be taken to authorization screen and enter your serial number.%) Quit Pro Tools LE and proceed and reinstall QuickTime.