Hello Sanket Singhvi,
RadContextMenu does not inherit from ContextMenu class so you cannot assign it to ContextMenu property. This property comes from a base class and expect a System.Windows.Controls.ContextMenu class.
You can see how to use RadContextMenu in our demos:
As for your second question - we are unable to reproduce it. Could you send us project that we can investigate?
the Telerik team
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