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<?php
/**
 * Gravity Wiz // Gravity Forms // Prevent Form from Being Updated
 * http://gravitywiz.com
 */
add_action( 'check_admin_referer', function( $action, $result ) {
	// update the "723" to your form ID
	if( $action == 'gforms_update_form_723' ) {
		die( 'Back up off my form, BRO!' );
	}
} );