"Some of the required files are missing" error when opening iTunes 7.5 or Error -2093 error when opening QuickTime Player 7.3

Issue or symptom

After updating to QuickTime 7.3 and iTunes 7.5, the following error message may appear when opening iTunes:

"Some of the required files are missing."

When opening QuickTime Player, an error -2093 may appear.

Solution

Remove any copies of iTunesSetup.exe that are currently on your hard drive. Then, download and install a fresh copy of the iTunes 7.5 installer (which includes QuickTime 7.3) from here:
http://www.apple.com/itunes/download/

Important: Information about products not manufactured by Apple is provided for information purposes only and does not constitute Apple's recommendation or endorsement. Please contact the vendor for additional information.