Having problem with Email Reminders

I work the helpdesk in my IT Department. We have a coworker here who’s email reminders in Outlook 2003 are not working. He sets reminders flags them dates them. Some come up some don’t. I did a test in setting up two different emails to go off the sametime. One came up one didn’t. I need to find a solution. Anyone else have these issues?

Thank You any help is appreciated.
Karla