The built-in layout persistence of RadDock does not include the content of the dock controls. If the referenced ascx control that you mentioned is loaded in a dock, the serialized dock state will not contain it by default so there should be no errors.
This, however, means that you need to store the state of the content of the docks separately, otherwise the web user controls you are loading in the docks will not be persisted. For example, the following demo of RadDock has loading of user controls in the docks and the name of the loaded user control is kept in the Tag
property of RadDock: http://demos.telerik.com/aspnet-ajax/dock/examples/myportal/defaultcs.aspx
When a dock is recreated, the correct user control is loaded via the information in the Tag property.
If the example in the demo does not meet your requirements or if I misunderstood you, please describe your scenario in greater detail. Are you using the same approach as the one in the demo for persisting the dock state in your project? Is the referenced ascx control loaded in a dock or somewhere else?
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