Hello Christian Surieux,
The reason for the problem is that ItemsRequested event is a result of a callback. And when it is executed the ViewState is not loaded yet. And yes,that is the reason why the Context property is implemented.
Please follow the article for more details : Passing Context Information to the Server
As for the second problem -you can use try-catch block
to catch the exception in the ItemsRequested event.
Also you subscribe to the OnClientItemsRequestFailed
event of RadComboBox and hide the default error message that appears in the combobox and display your own message instead
Hope this helps.
the Telerik team
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