You tutorials and install documentation are incomplete because they leave out many of the details like using directives. I have no doubt you've left out something critical that is causing the error above.
My view has:
@Html.DayPilotGantt("Mission", new DayPilotGanttConfig
BackendURL = Url.Action("Backend", "Mission")
The controller is boilerplate from the tutorial--with the missing Using directives lifted out of the downloaded tutorial (for both the view and the controller).
Line 41 is where the error occurs, and it has:
var v=new DayPilot.Gantt('Mission');
I saw a similar bug report from years past and the response was completely inadequate for something this expensive. I expect more details than that.