Default HELP! "E:Cannot Mount '/data'"

For some reason, out of the blue, I cannot read/write//mount my internal storage. I installed an unofficial version of CarbonRom on my Verzion M8 and everything was PERFECT! I created a Nandroid Backup of the way I had my CarbonRom setup and installed CHECKM8's aosp kernel to see if it would boot. It did boot, but was crashing all over the place. So naturally I went back into recovery to just restore my backup and all my internal data was gone. I've tried many things and I haven't been able to get my data to mount again.

HELP! As my phone sits right now, its a brick.

Basically, how do I restore access/mountability of the /data?

I tried fastboot erase userdata but it can't mount the data to erase it.

Going to try flashing the stock RUU and see if that'll do it. Currently downloading.