I have been having this problem since I tried to download the latest version of Itunes and safari. I am not sure whether this is a coincidence or not. I have a windows vista pc.
It appears that I no longer have administrator status on my stand alone PC which has only one user account (ie: administrator) I tried to uninstall Safari via control panel which gave me the error messgage that I did not have administrator status. I then tried to uninstall a couple of other programs with the same result.
I then searched the internet to find an answer, the most helpful of which appeared to be deleting hotkeys from the registry (that were put there by safari). When I tried to access thre Regedit program I got the message "The system could not find the environment option that was entered". I have since a system repair from the vista CD which only gave me the same error message. It would appear if I try to open any program that requires an administrator status I cannot do so.