Typically, this is due to information being entered under one login and attempting to view it with another login.

Starting with Hallmark Card Studio 2008, there is a separate Event Planner file for each account on the computer. In previous versions, the Event Planner was shared with all accounts. This meant that you could log in with your account, enter information in the Event Planner, log into another account and view that information. This is no longer possible with Hallmark Card Studio 2008 or later versions. If you enter information under your account, you need to be in your account to view that information. 

This will also affect the Reminders. If you entered a Reminder under your account, you will not receive the Reminder message, unless you are logged in with your account. If you need the Reminder to appear no matter which account you are logged in with, you will need to enter the Reminder in the Event Planner under each account.

So, if you have multiple accounts on your computer and cannot see the information entered into the Event Planner, it was most likely entered under a different account. In that case, you will need to log into the other account to view the information.