Security Check Failed Error

email subscriber not sending:
i am trying to send mail to all subscriber but after select subscriber group it shows “Security Check Failed” error message.. we have plugin up to date.
please help me
this code generate error “if ( ! empty( $_POST ) && ! wp_verify_nonce( $_REQUEST[‘wp_create_nonce’], ‘sendmail-nonce’ ) ) {
#die(‘<p>Security check failed.</p>’);
}”
file path is:
“email-subscribers/sendmail/sendmail.php ”
Please tell me how to solve it..
i want plugin builder support