Assigning admin invalidates the user

I am experiencing an issue as I am following the tutorial and
currently at the end of chapter 10. When I use toggle in the rails
console to flip the admin property of a user from false to true (I'm
trying to create an Admin user), I am successful in doing so, however
that user becomes invalid, when I try to log in to the application
with this user's credential I am getting an error that the credentials
are incorrect (even though they are) ... just from checking the logs
and the looking at the terminal, it seems the authenticity token is
either missing or incorrect... any ideas what I am doing wrong here? I
tried following the tutorial as close as possible, I doubt I missed
something, but its obviously possible..

Thank you and best regards!

There are lots of tutorials out there. Please be more specific as to which one you were following. For example, give us a link to it.