When side loading apps, taping "install" does nothing

This has happened twice. Once when I saw Hangouts has an APK update that I wanted to install instead of waiting for the play store and now trying to create an APP from Tasker. I get a install screen (attaching screen shot of install screen) but when I tap Install, nothing happens. Tapping cancel works, just not install. I checked Security and I have allowed Android to install from unknown sources.

Ideas? And thanks.

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