What is the name and path of that script? Is it being executed from Cron? Or is it possible that it’s being executed in response to receiving an email?
Looking through the auto.pl script that comes with Usermin, it looks like that script is used if the user sets up a scheduled deletion policy for their mailboxes.
For example, if a user wanted to make it so that their trash folder deleted all email older than a week, they could do that.
It’s possible that a deletion policy was setup for a folder that no longer exists. You could certainly safely remove that entry from cron if you like.