Ok looks like I figured something out by looking at the other postings in this forum. It has something to do with the cron scripting. If you go under Site Administration>Notifications, you should see a line that says "The cron.php.maintainence script (or something like that) has not been run for the past 24 hours". Click on the link and the cron maintenace would run and it will remove any enroll expired entries. This booted out all the students whose enrollment has expired. I am checking whether this needs to be manually performed each time, hopefully not, but I will report back if I find anything new.