iMac firmware won't update

[Gherkin]

I have an Intel iMac. There was just a firmware update about a week ago, but I didn't install it until right now. I shut the computer down as it says, but when I restart, it just comes back up with the same dialog as before the restart, and the firmware is not updated.

What should I do?

 

[emptyCup]

You got this from Software Update so you know the update is for your machine, right? If so, try again making sure you are following the directions. If it still does not work either call Apple or post complete info about which update and exactly what machine you have here.