I have a machine running Windows 7 and recently, when attempting to install an update though Windows Update, I received the message, Error 80240016, Windows update is currently installing other updates. Please try again later. I had gotten this error message before and solved it by restarting Windows. But not this time.
A quick search at Google identified a solution that worked. It turns out that if Microsoft Security Essentials is running a scan, this can prevent updates from being installed! And, I guess, this produces a completely inaccurate error message in Windows Update!
I checked and, although Microsoft Security Essentials was not running a scan, it was warning me that a scan had not been run in a while and my computer might be at risk. I let it run a quick scan, then tried Windows Update again and, this time, it happily installed the pending update.