You encountered the following error at design-time:
Error Creating Control - [control id]
'' is not a valid identifier.
When a WebDock or a WebSplitterContainer is located within certain templated controls, such as a Wizard control or an AJAX TabContainer, the panels within the WebDock or WebSplitterContainer must have valid IDs.
The relevant panels include:
WebDockPanel
WebDockUpdatePanel
WebDockPanelGroup
WebSplitterPanel
WebSplitterUpdatePanel
Normally, the ID of the above panels are optional.