I got the very same problem. Would be great if there would be a fix sometime? Have to move websites from one server to another server fromt time to time.
This problem seems to be new, because otherwise a migration usually went smoothly (deactivate full-WAFF mode, deactivate Ninja Firewall and uninstall. After the migration, reinstalling the Ninja Firewall always went smoothly)
Edit: After deleting /wp-content/nfwlog, I was able to activate it properly. Thanks SHAO!!!
