Default Screenshot button combination not working

It may be a simple issue to fix, but it's annoying that I can't capture my screenshot the power button and volume down combination capture screen. I'm having to go to power menu and selecting screenshot.

Any thoughts as to how I get it back to default?

I'm using Paranoid ROM 4.1-Beta 2.

Sent from my Nexus 5 using xda app-developers app
Retired
> Heaps of Nokia Phones > HTC Desire > iPhone4 > Samsung Galaxy S II > Samsung Galaxy Nexus Prime > Samsung Galaxy Note 1 > Galaxy S III > Galaxy Tab 2 7" 3G > iPhone4s

Current
> Google Nexus 5 32GB
> Samsung Tab 2 10.1 Wi-Fi