It seems to be a problem on the client side. Is it possible that the reminders are turned off? Little chance.

1. Check if all reminders flags are 'Turn on'.
On the Tools menu, click Options.
Click the Other tab, and then click Advanced Options.
Click Reminder Options.
Select the Display the reminder check box.

2. Reminders are Turn On but reminders are not displayed when the event
comes due.
On the Tools menu, click Options.
Click the Preferences tab, deselect (uncheck) the Default Reminder check box
and then click Apply.
Redo the operation by selecting (checking) the same Default Reminder box
and click Apply.