How to Fix "Sys.ArgumentTypeException: Object of type ‘Sys._Application’ cannot be converted to type ‘Sys._Application’." Error

In one of my client projects, we kept seeing this error, and basically ignored it for a long time. In our case, we saw the errors specifically on pages that included NewsGator Web Parts and we thought they might be the problem, but it was actually a problem with the SharePoint AJAX settings which NewsGator would…