In the versions before 2011.Q3.Beta (2011.3.1020), RadRichTextBoxWibbonUI was based on RadRibbonBar, but starting from the version in question, it uses the new RadRibbonView instead. The advantages of using the new control compared to the old one are described in detail in this blog post.
The two controls cannot be used in the same project, so you need to remove the reference to Telerik.Windows.Controls.RibbonBar. You can also refer to this article for a walkthrough on upgrading a Q2 project to Q3.
If you meet any difficulties, we would appreciate a sample project illustrating the issue.
the Telerik team
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