Strange iCal

Hello…

When I create a new event in iCal, edit it, and then click the X to close the window of that event or click on something else in iCal, the changes that I've done to that event just disappear, sometimes that doesn't happen but most of the times it does. Most of the times iCal accept my changes but after just a few seconds, that's canceled and it shows just the default text.

What can i do?