MySQL max user connections

[trophiesonpsn]

We keep getting the following error:

Database error in vBulletin :

mysql_connect(): User xxxx already has more than 'max_user_connections' active connections
/var/www/vhosts/xxxxx/includes/class_core.php on line 317

It is always a different IP except for microsoft's crawler always seems to trigger this even when instructed to crawl late at night.

I should say we are aware of the setting for persistent connections and aware of the limit (but it is set very high - supposedly at 100) and we do not have a big forum at all right now. We are even on a larger than average VPS.

It doesn't make sense that we would be reaching this limit and it makes me wonder if there is anything additional that could be occurring that is keeping connections open and how we might check.