The onliest reason we can find reasonable for such error is if you missed to add reference to Telerik.Windows.Controls.dll in your project. The required assemblies for RadRibbonView are listed in our documentation - here
. If you have everything correctly added and you still face the same issue, please try to use the CLR namespace - xmlns:telerikRibbonView="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.RibbonView"
instead of telerik schemas.
You might also open a formal support thread and send us a runnable sample with all binaries included so that we can inspect locally what might cause the problem.
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