The error reads:
Cannot unregister UpdatePanel with ID 'SupNavBar' since it was not registered with the ScriptManager. This might occur if the UpdatePanel was removed from the control tree and later added again, which is not supported.
However such errors are not commonly encountered, therefore I would suggest to recreate the master file, using the guidelines from the provided link. Also please note that the ScriptManager must be the first control added to the runat="server" form if you are using a masterpage.
Also please note that Sitefinity has the ability to inject ScriptManager if your control requires it. You can decorate your user control with the below attribute so that Sitefinity knows that this user control needs a ScriptManager:
public partial class WebUserControl : System.Web.UI.UserControl
This is generally a better approach to use the ScriptManager. If you do not have controls that need it on your pages it will not be included (improve page performance by not loading unnecessary scripts).
One another user however, who encountered the problem managed to resolve it. Here is a quick quote on his notes:
"It looks like the cause of this bug was that I was using a page template which contained a billing summary (expanded) that inherited another page template with a billing summary (expandable). Changing the billing summary on the child template to the link version causes this error not to occur."
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