I have prepared a sample application which has a Telerik TabStip with a basic example of EditForm. You can see that project as an attached file. Could you run it locally and if it works as expected for you, compare it against your own and see what are the differences that cause the issue. If this does not help you move forward, could you modify the application so that the exception is reproducible and send it back to us so we can dive deeper and suggest another solution?
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