Setting initial RadioButton selection in RadioButtonList

Hi all (and @enchev),
I didn't want to open a new title.

I added a RadzenRadioButtonList on the page (The TValues are int).
When I try to specify the initial value the following error message appears on the screen.

I checked out the code, there were no error messages. While the code is running everything is as expected and RadzenRadioButtonList is working properly.

Am I missing something or is this a bug?

Thanks for your support.