Update Panel error: Control with the ID “xxx” could not be found in the UpdatePanel

Question

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

Answer 1

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.