Do you have a number in parenthesis following your calendar or tasks folder name? This means you have an unread item in the folder, generally a meeting or task request. To find out, run advanced find on the folder and look for unread items or use the by category view and browse.
If you don't care what they are and just want to mark them read, right click on the folder name and choose Mark All as Read.
Published August 10, 2004. Last updated on May 16, 2011.