Your clients do not have to install RadControls for WinForms on their computers. Our WinForms controls should work flawlessly with whatever deployment you have set up for your WPF apps, so far as those are not WPF browser applications /compiled XBAP files/.
The issue in Michael's case was most probably related to the fact the developer did not have RadControls for WinForms installed on his machine.
All the best,
the Telerik team
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