"Email My Activities" not working

Hi, I recently run into this issue where one of my colleagues Zoho Projects account stops sending the "work task reminder" to the user. The last notification mail received is on 27 May 2011 but no changes are made to the settings.

I even tried to update the reminder time for a few times but still did not receive any mail.

Anyone has an idea what went wrong and how to fix it? Thanks.