🙂 Many thanks. Best to print off a copy of these instructions, because at one stage of proceedings you won't be able to use a web browser.
Preliminaries
Switch "Run as administrator" off in the QuickTimePlayer.exe compatibility tab.
Download and save a fresh copy of the QuickTimeInstaller.exe (installer file) from the following page. Get the option that
doesn't mention iTunes. Don't run the install on line, and don't start the install just yet.
http://www.apple.com/quicktime/download/
Now quit all of iTunes, Safari and the MobileMe control panel if you have them installed and open. (They all use AAS, and may interfere with the uninstall if left open.)
*Uninstall phase*
Head into your Uninstall a program control panel. Uninstall QuickTime. Uninstall Apple Application Support.
(From this point, none of iTunes, Safari or the MobileMe control panel will launch until we reinstall AAS, which should happen when we reinstall QuickTime.)
Next we'll remove any leftover program files and folders.
In "Computer" open "Local Disk C:" (or whichever drive you have your program files installed on).
Open the "Program Files" folder.
Right-click on the "QuickTime" folder (if it still exists) and select "Delete".
Open the "Common Files" folder.
Open the "Apple" folder.
Right-click on the "Apple Application Support" folder (if it still exists) and select "Delete".
In "Computer" open "Local Disk C:" (or whichever drive you have your operating system installed on).
Open the "Windows" folder.
Open the "System32" folder.
Right-click on the "QuickTime" and "QuickTimeVR" files (if they still exist) and select "Delete".
Empty your Recycle Bin.
(If you got any error messages on the uninstalls and/or deletions, let us know what they say. Precise text, please.)
*Reinstall Phase*
Restart the PC. After the PC restarts do not open any applications. Disconnect from your network and/or the internet. Now switch off all your security software (firewall, antivirus, antispyware).
Now start the reinstall by doubleclicking the QuickTimeInstaller.exe file you downloaded earlier. (This should also reinstall Apple Application Support.)
Reenable all security software prior to reconnecting to your network and/or the internet.
... does QuickTime launch without the error this time? Or do we still have to do the "Run as administrator" thing?