If you have Spybot installed, go to the "Immunize" page and scroll to the bottom (most people don't and never even know theu're there) and you'll find three tick boxes. Make sure the third one, "Lock IE control panel against opening from within IE (current user)" is
not ticked.
If that and the other suggestions above, don't work, Try here:
Restrictions Error Message. Not sure about the providence of this, but perhaps worth a try.