Ok, since both of those seem ok I guess it's not a problem with it querying the table, so maybe it's something with the way they are joined.
Try this query and see if it's any better...
PHP Code:
$pollinfo=$DB_site->query_first("SELECT poll.pollid,poll.question,poll.dateline,poll.options,poll.votes,poll.active,poll.numberoptions,poll.timeout,poll.multiple,poll.voters,thread.pollid,thread.open FROM poll LEFT JOIN thread USING (pollid) WHERE thread.forumid=$pollsforum ORDER BY poll.dateline DESC LIMIT 1");{