Editing uEnv.txt to disable HDMI causes BBB to stick in uBoot and I have to re-install sys.

Everyone says you can edit uEnv.txt while connected to the USB, which is true. But!!! When I reboot the systems fails and is stuck in uBoot.
All I want to do is disable the HDMI, uncommenting the line in uEnv.txt isn’t working for me.
Any suggestions?