vsftpd keeps stopping
 

I'm running CentOS 4.4 with vsftpd and Zimbra Collab Suite. It seems that every few days, vsftpd stops running and requires a manual restart. I don't know if this is because of something conf wrong or if this has to do with an outside attack. Prior to installing the Zimbra Suite, I had not had a vsftpd issue across distros for years.