Thank you for contacting us.
Actually this error rises for some different reason. Even more there is no a clear reason for it.
In the points below we summarized some particular cases all related to this error:
- Check the target version of our RadControls library.
- Clear the reference to the System.Windows assembly and reference it again.
- Check your Xaml code for typos as it is described in this link.
- Preview following links: link 1, link 2, link 3, link 4.
We hope this information will help you.
the Telerik team
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