Quicktime 7.x installed under Windows XP (admin account). It worked, installing updates, too. After upgrading the system (no clean install) to Windows Vista Business (same admin account/UAC off) Quicktime still worked. Hoped to fix some smaller issues with the newest Quicktime 7.1.5 Update.
BOOM!The Application didn't start any longer. Giving an error message saying "Error 46: Could not find or load activex control" (only the browser plugin worked fine). Uninstalling/Reinstalling didn't help. Apple's installation package installs Quicktime in such a way that it only functions at all under the actual account you were logged into when you installed it. The Upgrade from XP to Vista with the new User Account Control (even when turned off) messed up things here, the problem: you can't even correctly uninstall Quicktime in this state. (Update Jul 2008: Since the first Vista-capable release 7.2 of Quicktime, a fresh install on Vista should work smoothly. But once you've 'infected' your registry with an older version of QT that's not Vista compatible, then all subsequent installs will give you the Error 46.) A similar problem is described here. But the fixes didn't work for Vista. But based on Bazm's post there, I came up with the following solution for Vista to reset necessary registry key permissions:
The solution: There is an old NT utility called SubInAcl.exe that can be used to reset permissions in Windows XP and also in Vista.
Step 1: Vista's User Account Control (UAC) must be disabled for these steps to work (Control Panel -> Turn User Account Control Off). You may enable UAC back on after these steps. And you should run this as admin. Step 2: Download subinacl.msi from Microsoft and install it. Step 3: Download my modified version of reset.cmd from here and save the file in 'C:\Program Files\Windows Resource Kits\Tools'. Step 4: Open Command Prompt and type the following without quotes (hit Enter):
'cd c:\program files\windows resource kits\tools'
Step 5: Now type 'reset.cmd' and hit Enter (without quotes)
You will see the Command Line Tool running for some seconds. The issue should have been fixed and Quicktime should run again.