I am sorry to hear that you are experiencing troubles when using the RadControls through the Toolbox.
The problem that you have encountered is strange and we haven't seen it before. Can you try whether resetting the Toolbox (right-click the Toolbox and select 'Reset Toolbox') solves the issue? I also suggest you restarting the IDE.
If the this doesn't help I suggest you to repair your RadControls installation.
I hope this helps.
the Telerik team
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