Outlook 2003 – Calendar has a new item

Hello everyone,
I have a user here who has a 1 next to his calendar. Its just like when you have X number of unread email messages. Why would calendar display 1 next to it. This happens on his desktop and also when he logs onto his laptop. Honestly speaking, I haven’t had a chance to research this issue too much, I was just hoping one of you experts out there would know.
Thanks in advance.