SMS Problem - Moto G update 4.4.4
I see this issue quite frequently.  Hangouts will crash if you disable stock Messaging app, but you can't re-enable the Messaging app if you've disabled it before upgrading the OS.

In order to resolve you need to go into Settings -> Apps, tap the three-dot menu button, and select the "Reset app preferences" option:


This re-enables all previously disabled apps, including the ones you couldn't re-enable before.  Hangouts should also stop crashing now.