My S4 is stock 4.2, but rooted, VRUEMK2 build, for reference.
I need to encrypt my device to use my corporate email, however, it keeps failing. Basically, to go step by step, I set up a PIN screen lock, connect my charger, input my PIN, and hit encrypt... I see the green Android dude for about 10-20 seconds, my phone reboots, and I'm back at my lock screen. No encryption applied.
I've done around three to four factory resets and it still doesn't work.