This afternoon, I upgraded from QuickTime 6 to QuickTime 7 on my Windows XP Professional machine. When I tried to use QuickTime from a user account it gave the following error message:
Error 46: Could not find or load activex control
A little Googling led to a solution suggested by Gerhard Schwoiger ("Ger Ger") here (see under "Apple QuickTime 7.x Annoyances"). I implemented this solution from an administrator account. This fixed the problem.