I can totally understand your frustration to spend hours in searching one RadComboBox that throws an exception.
I am afraid that printing the RadComboBox name or any any property of that object could not be achieved in this case. I would recommend debugging the server-side code and specifically the data bind expression for your RadComboBox controls and try to find which will have invalid values.
I also forwarded your proposition to our developers for consideration.
I would like to apologize for any inconveniences caused.
the Telerik team
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