iTunes update

I've been trying to download the most recent update for a long time. I thought I had fixed the problem as I was able to install the last update, but it seems the problem has come back. It says I that the administrator has set permissions to stop the installation, but I am the administrator, and I've checked the permissions, which say I should have full control. I have tried downloading and then manual installing, as well as downloading directly from the website. I've also re done the permissions and created another administrator, which still doesn't work. Please help!!!