The RadDocking control currently doesn't check whether the layout is loaded correctly or not - it tries to load what is given. Anyway, you could use ElementLoading and ElementLoaded events in order to find out which element is loading/loaded. Please, refer to the following article where you can find more information - http://www.telerik.com/help/silverlight/raddocking-features-save-load-layout.html
Hope this helps.
the Telerik team
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