HTC made a small change in the 2.2 ROM version : to edit an event from the event detail page, you have to make a long press on it …
sources :
http://androidforums.com/evo-4g-support-troubleshooting/151719-cant-edit-calendar-events-after-2-2-update.html
http://androidforums.com/evo-4g-support-troubleshooting/164636-2-2-users-there-edit-event-your-stock-calendar-app.html
