Quoted from http://research.gerger.com/?view=lab&aID=1006:
Apple Quicktime 7.x Annoyances
"Error 46: Could not find or load activex control"
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. 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: Download subinacl.msi from the link
http://go.microsoft.com/fwlink/?LinkId=23418 and install it.
Step 2: Download my modified version of reset.cmd from here and save the file in 'C:\Program Files\Windows Resource Kits\Tools'.
Step 3: Open Command Prompt and type the following without quotes (hit Enter):
'cd c:\program files\windows resource kits\tools'
Step 4: 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.