Please email it to support@mindfusion.eu. For now you might try to load a hidden diagramview initially and when the button is clicked just make it visible.

The problem happens because the control uses ClientScriptManager.RegisterHiddenField() to create a few hidden elements in the page DOM and post back through them various information about what happenned on the client side. Apparently the page content outside of the update panel cannot be modified from within the context of an UpatePanel asynchronous update, so the hidden elements do not exist on the page and you get the JS error. Now you can fix this by adding the fields to the update panel, e.g.

DiagramView1.ID = "dv";
HtmlInputHidden h1 = new HtmlInputHidden();
h1.ID = "_mfusion_dv_ClickedItem";
UpdatePanel1.ContentTemplateContainer.Controls.Add(h1);

However there's a bigger problem; the control calls Page.RegisterRequiresPostBack(this), which also does not work from within an update-panel event handler, and the posted-back diagram is lost. Our developer will research if there is some official way to register controls for post-back processing when added to the page in such a way.

Stoyan