Calendar (12) - Calendar shows 12 unread messages

I'm having a strange problem with my Calendar since a collegue sent me a
meeting request as a .ICS attachement. Since I saved it to my calendar it
shows that I have unread messages in my outlook calendar. I've performed
advanced finds on the calendar, i've even wiped out all contents of my
calendar but the calendar always shows (12) unread items. We are on an
exchange server and my e-mail is setup directly on the mailbox. I tried
opening my outlook through "Web Access" and it also displays 12 unread items.
Does anyone have an idea of how to get rid of these unread items? Thanks