su -l root permission denied

I have centos7 as a virtual box on windows 7. Besides root, I created another user "john" during that time. Some time later, I forgot my root password and reset it my going to single user prompt. Since then whenever I login as "john" I am not able to do su -l root. I get permission denied. I logged in as root and changed sudoer file with the following: root ALL=(ALL) ALL admin ALL=/bin/su Defaults: admin rootpw john ALL=(ALL) ALL I then added john to wheel group and updated /etc/pam.d/su with: auth required pam_wheel.so use_uid Also,I am not able to do su -l john when I am logged in as "root". Any help here is appreciated. /var/log/secure shows: Mar 6 .... localhost su: PAM(other) no module name supplied Mar 6 .....localhost su: PAM(other) illegal module type: @include Mar 6 .....localhost su: PAM pam_parse: expecting return value: [...common-session] Manny