I had to do this once. I opened Outlook on my pc, deleted all items from the list view. Changed my sync options to sync FROM the pc TO the Storm (1 direction), resynced, then changed the sync settings back.
There may me an easier way, but this worked for me.
Whatever you do, be sure to backup your Storm 1st.
open Desktop Manager. Got to Backup and Restore, then Advanced. Choose your calendar on the right, highlight it then hit clear.
When you say calendar do you mean the calendar as a whole or just the entries in a specific calendar..
When I got the new facebook application it took over and deleted all my dates and added facebook b-days.. I put some of them back in my calendar and they are all gone again.. I want to make the facebook calendar go away forever.. I lost so many appointments in there, and I called all the places and got my appt dates again, added them again and now they are gone