Currently Being ModeratedFeb 20, 2013 6:55 PM (in response to aad440)
I had a similar problem. My calendar is on an Exchange server, so my solution may or may not work for you. Try double clicking on the grey event, select Edit, change anything in the event (e.g., add a period, change the alarm), close the editing window, and then select Refresh Calendars under the View menu. May not work, but it can't do any harm.