I have no idea why iTunes stopped working for me suddenly. It would not load, and when trying to update it, I received various Quicktime install, can't remove errors. The procedure below from weiseguy1 worked perfectly. Thank you for saving me countless hours of angst!
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If you’re trying to install iTunes on Windows and it fails during the Quicktime installation with a “-3? error, or you try to install Quicktime 7.0.3 on Windows and you get an Error 1714 or some complaint about not being able to find quicktime.msi even though it’s there, the way to fix it is to:
*Start/Run regedit
*Navigate to HKEY_CLASSES_ROOT –> Installer and select Products
*Use the Edit/Find menu to find quicktime inside that part of the key
*Delete the whole branch of the tree just ahead of the key where you found quicktime.msi
NOTE: I first tried deleting just the key with quicktime.msi and got the same errors so you have to delete the whole branch ahead of the key that contains quicktime.msi. I can’t remember the name of the folder but there was about 3 sub keys in it that got deleted in the process.
IT WORKS !! You should now be able to install Quicktime and iTunes without incident.