PHP Warning: Illegal string offset 'usergroupid' in

[oldengine]

Admin Control Panel (vBulletin 3.8.11) PHP 7.1

[08-Sep-2019 18:18:50 UTC] PHP Warning: Illegal string offset 'userid' in /home/smoky/public_html/forum/includes/functions.php on line 439
[08-Sep-2019 18:18:50 UTC] PHP Warning: Illegal string offset 'userid' in /home/smoky/public_html/forum/includes/functions.php on line 442
[08-Sep-2019 18:18:50 UTC] PHP Warning: Illegal string offset 'usergroupid' in /home/smoky/public_html/forum/includes/functions.php on line 382
[08-Sep-2019 18:18:50 UTC] PHP Warning: Illegal string offset 'usergroupid' in /home/smoky/public_html/forum/includes/functions.php on line 448
[08-Sep-2019 18:18:50 UTC] PHP Warning: Illegal string offset 'userid' in /home/smoky/public_html/forum/includes/functions.php on line 448

These are likely to be in the calendar Plugin Event Attendance - show/enroll
The question is where?

//Check time till event
$time_until_event=$eventinfo['dateline_from']-(TIMENOW+$vbulletion->userinfo['timezoneoffset']*3600);
if ($vbulletin->userinfo['dstonoff'])
{
    $time_until_event=$time_until_event-3600;
}
//echo $time_until_event."   ";
$show['enroll']=(($time_until_event>0) || ($vbulletin->options['lateenroll'])) ? true : false;


//Enroll/Cancel
if ($_REQUEST['ea'] == "attend" || $_REQUEST['ea'] == "unattend" AND ($time_until_event>0 OR $vbulletin->options['lateenroll']) )
        {
            if (!$eventinfo['roll'])
                {
                    $roll = array();
                }
                else
                {
                    $roll = @unserialize($eventinfo['roll']);
                }

        if ($_REQUEST['ea'] == "attend")
            {
            if ($vbulletin->userinfo[userid])
            {
                $roll[$vbulletin->userinfo['userid']] = $vbulletin->userinfo['username'];        
            }
            else
            {
            print_no_permission();
            }
            }
            else
            {
            if ($vbulletin->userinfo[userid])
            {
                unset($roll[$vbulletin->userinfo['userid']]);        
            }
            else
            {
            print_no_permission();
            }
            }
    
            $eventinfo['roll'] = serialize($roll);
        $db->query_write("UPDATE ".TABLE_PREFIX."event SET roll='".addslashes($eventinfo['roll'])."' WHERE eventid='".$eventinfo['eventid']."'");
        $_REQUEST['do'] = "getinfo"; 
}


//show enrolled people
        $rollcount=0;
                if ($eventinfo['useroll'])
                {
                    // Roll for this event
            unset($rollbits);
                    $show['userattending'] = false;
                    if (($roll = @unserialize($eventinfo['roll'])) && is_array($roll))
                    {
                if ($vbulletin->options['roll_sort']) 
                {
                    uasort($roll, "strnatcasecmp"); 
                }

                            if (array_key_exists($vbulletin->userinfo['userid'], $roll))
                            {
                    $show['userattending']=true;
                            }
                    
                    while ($rollusername = current($roll)) 
                { 
                $rolluserid = key($roll); 
                eval('$rollbits .= "' . fetch_template('calendar_rollbit') . '";'); 
                $rollcount++;
                next($roll); 
                } 
                    }
                        else
                        {
                            $eventinfo['roll'] = "";
                        }
                        
                        eval ('$eventinfo[roll] = "' . fetch_template('calendar_roll') . '";');
            $eventinfo['event'].=$eventinfo['roll'];
                    // End Roll
                }
                else
                {
                    $eventinfo['roll'] = "";
                }