Error in Adding new Item with Combobox.

I am working with the good example of Editing custom editor under the MVC examples.
 It shows how to build a dropdownlist for use when editing a cell in a grid.
 I have to create a new post in the grid and I add the following to the file; Editing_Custom.cshtml:
 

.Create(create => create.Action("EditingCustom_Create", "Grid"))

.ToolBar(toolBar => { toolBar.Save(); toolBar.Create(); })
 
And I already get an error here before I come to do the coding in the .cs-file.
 When debugging with firebug, I get an error from javascript that says: ReferenceError: EnrollTypes is not defined.
EnrollTypes is the class that is used for making the dropdownlist.
 Could someone please give me a hint on what I have to do when creating a post in a grid with relational data?
 
I saw in some forum that Foregin key will sove this problem, but in my case there is no key column which can be named as foreign key. I just want to have a dropdown in grid column and it should also appear when I click on Add New Item button. 
 
Regards,
 Nitin