Hi,
1. Try to Login from OWA with the emal users , can you see reminders from there.
2. Outlook | Tools | Options | Other | Advanced Options | Reminder Options | please check whether the Display the reminder option is checked.
3.If the issue persists, please use MFCMAPI to delete the Reminders Folder, then run outlook /resetfolders to recreate this folder.
4.Try to recreate one users profile of the Outlook to check this issue. And make sure the Default Reminder option has been selected on the side of the sender.
5. try this Hostfix for Office 2010 SP1
http://support.microsoft.com/kb/2584053also check to see if the user has other email accounts they connect to with Outlook such as a shared mailbox or any other mailbox. The corruption could be in one of the other mbx's if so
Remember that both OWA and iPhone only access one MBX at a time- so multiple mailboxes could be the culprit