Error 403 for using wordpress functions

Hi,
In new update i can’t save any older codes (Php or Universal)
I think this problem is for using wordpress functions in code, For examples:

if ( is_user_logged_in() ) {
    $current_user = wp_get_current_user();
    if ( ($current_user instanceof WP_User) ) {
        echo get_avatar( $current_user->ID, 64 );
	}
}

After click on save button it returns 403 error page