I'm pretty sure it's working but your query is incorrect... I think it's taking the whole list and interpreting it as a string, rather than a list. Instead of this
Code:
WHERE eventid IN '" . $vbulletin->GPC['eventids'] . "'
use this
Code:
WHERE eventid IN (" . $vbulletin->GPC['eventids'] . ")
You may also want to do some more cleaning on that string, but it's not a big deal because it's in the AdminCP.