I am an administrator on my family computer. However so is my dad and gets the same error message trying to access Program Files.
However it is only the main folder that is not accessible, if I wanted to access spybot S&D's folder I could manually type C:\Program Files\Spybot - Search & Destroy and the folder will open no problem.
Any ideas? I have heard of "unlocker" a unlocking program but is this usable on such an important folder? If so, is it a smart decision?