I have a composite drop down calendar user control that consists of a textbox and and calendar image and a validation control. I expose a property called \"TextBox\" on the
You may want to try:
... trigger.ControlID = dtmDateFirstEntry.TextBox.ID trigger.EventName = "TextChanged" ...
that is, use the ID instead of the ClientID for the ControlID and do not use the "On" prefix for the EventName.