I found the following solution for Vista and XP here:
http://research.gerger.com/?view=lab&aID=1006
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
http://gerger.com/o/assets/x/?id=22540 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.