Have you overridden or edited the Event page type? It displays the event description in the Main area, so if that's not present, the description won't show. The file is calendar_event.php and it's normally located in packages/calendar/page_types/

Otherwise I'd recommend clearing your site cache from Sitewide Settings > Speed Settings and see if that helps.

No, I haven't edited or overridden the page type as far as i know.
This used to work when I installed it about 10 months ago.
There's been a Concrete5 update and a server php 5.3 update in between and its been running ok since those updates.
My customer just notified that it has stopped working.

The first thing i tried was to clear the cache. Didn't help.

Could it be the number of created events? (+100)

Can you send me a private message with the site URL plus admin login and password? I can check it out for you and try to figure out what's going on.