"Updater process ended with error: 7" when flashing.

I am trying to flash Viper on Marshmallow. I have had it flashed before and it worked fine.
Now I am getting this error and don't know what to do.
What does this error mean and how can I fix it?

Sent from my Nexus 9 using XDA-Developers mobile app

from xda-developers http://ift.tt/2bWLlEU
via IFTTT