OS X 10.11 unable to press "allow" on Keychain Access dialogs
I encountered this same issue today. I could not "Allow" or "Always Allow" any programs, nor could I confirm my password in any dialogues. The interface wouldn't shake, even if I had entered the incorrect password.

I use Synergy to facilitate programming over several different computers. My mouse and keyboard do not belong to the Mac OSX device. I was able to hit the "Allow" button once I used a mouse actually hooked up the Mac OSX device.

In general, try turning off any virtual or physical KVM services and use the Mac mouse/keyboard directly.

Hopefully this can help you or someone else who comes here looking for help.