ASP MVC5 to MVC6 conversion - problem with [ComboDataSourceAction]

Hi, I am converting my existing working project from MVC5 to MVC6 by creating a new MVC6 project and moving things over bit by bit.

I have run into a strange issue with [ComboDataSourceAction].   In my old MVC5 project it works fine, but in my new project it returns different JSON (just containing the IDs, not the text I want to display):


public ActionResult ClientComboData()


IEnumerable<ClientName> clientNames = GetClientNames();

return View(clientNames);

//return Json(clientNames);


If I swap in the commented out line, it seems to return Json with the names included and display them in the combobox and the drop down list shows them correctly but when I type anything in the autocomplete I get the following error:

Unhandled exception at line 26, column 4876 in http://localhost:62643/ignite ui/js/infragistics.lob.js Unable to get property 'locale' of undefined or null reference

Here is the class it is serializing:

public class ClientName


public int ClientId { get; set; }

public string FileAsName { get; set; }


Here is the content of the JSON when I hit F12 in IE and look at the network traffic.


How can I fix this?