Can't Flash Recovery After Updating to 6.0

I've used numerous guides and attempted to flash EITHER TWRP or CWM using fastboot. The process appears to work without any issue, but when I try to reboot to recovery, I get the lovely droid with the red icon.

For some reason, TWRP manager crashes immediately when I attempt to initiate an install of the recovery from within the app (I'm now on the rooted ROM from Bad Boyz).

Am I missing something obvious?

Thanks