Error: Sys.InvalidOperationException: Two components with the same id 'xxx' can't be added to the application.
This is a conceptual problem in RadDock. You can reproduce it by creating a simple page, containing the following markup:
<asp:updatepanel runat="server" id="UpdatePanel1">
<telerik:raddockzone id="RadDockZone1" runat="server">
<telerik:raddock id="RadDock1" runat="server" autopostback="true" dockmode="docked">
<telerik:raddock id="RadDock2" runat="server" autopostback="true" dockmode="docked">
Now, grab one of the RadDock controls and drag it. When you are dropping it, if you are fast enough and you succeed to grab the other RadDock control without dropping, you will be able to get the exception. On localhost this is quite hard to be fast enough, but on production sites it should be relatively easy for the fastclickers.
The problem is related to the fact, that when you grab a RadDock control its HTML element is detached from its parent. When you drop a dock, it initiates a postback because of the AutoPostBack property (converted to AJAX call by the UpdatePanel), the UpdatePanel is updated and since on the server it contains the grabbed RadDock control, it adds it to its HTML. On the client it does not contain HTML element for the grabbed dock, its client-side object is not disposed and newly added dock generates the exception.
Workaround: use UpdatePanel controls with UpdateMode=Conditional. When you are adding/removing RadDock controls from the zone call the UpdatePanel's Update() method to force it to refresh its content. When you are just moving the docks don't call the Update() method and you will avoid the exception.
This is the only way we were able to reproduce this problem until now. If you can reproduce using different steps, please, open a new support ticket and send us a simple application. I will try to find a workaround or a solution ASAP.