With my experience on 7S and TTG... I'll bet 5 bucks you are either:
A. Not running as Admin.
B. Closed Unturned instead of playing it..
C. Don't know to click Insert to get the menu to open.
D. Forgot to add the error message in your original post as a screenshot or video so we could even figure out what's going on.
E. You're using a MAC or Linux in which case I have no advice for you.
F. Your Anti-Virus is screaming "Oh no trojan!" and deleting it before you can even inject.
G. Decided not to follow everything literally step-by-step.
I haven't heard of anyone getting such an error message before.. I would suggest to go through the steps again, possibly video tape it or at least a screen shot.