Not allowing Widget Upgrade

I received this note when trying to upgrade the Widget "cartoons" software after clicking on their "upgrade" link: "cartoons.wdgt" can't be opened because it is from an unidentified developer". "Your security preferences allow installation of only apps from the Mac App Store and identified developers" Yet this was downloaded years ago from the Apple's Widget list. I also find nothing in general or Safari preferences that deals with limits on downloading applications.

Any idea what is going on?