Error at Login - "The action you requested is not allowed

I recently copied my website from one domain to another. Unfortunatley, login does work anymore. In the session dir, I can see this the ci_session txt file:

__ci_last_regenerate|i:[snip number];error|s:40:"The action you requested is not allowed.";__ci_vars|a:1:{s:5:"error";s:3:"new";}

Not sure how to debug this or the meaning of the error message. Any pointers appreciated.

When I moved over the site, I did delete all session ids.

Running https only on both sites.