Outlook Calendar - Cannot save item. Unknown error

I was having an issue with one mailbox calendar. Couldn't add or modify items.
In Exchange 2000 I used a tool to find corrupt items, I am not sure how to with Exchange 2007.
My best bet was to find out the last item added to this mailbox and deleting it.
After deleting 2 items, I was able to create one and modify others.
Still not sure why this happened, but this is FYI if anyone else has the same issue.