I'm trying to use a combo in a grid as follows:

@(Html.Infragistics()
.Grid(Model)
.ID("grid1")
.PrimaryKey(nameof(LuItemType.ItemTypeId))
.UpdateUrl(Url.Action("UpdatingSaveChanges", "ItemType"))
.AutoGenerateLayouts(false)
.AutoCommit(true)
.Columns(column =>
{
column.For(x => x.ItemDesc).HeaderText("Description").DataType("string");
column.For(x => x.SafeWorkingLoad).HeaderText("SWL").DataType("string");
column.For(x => x.InspectionPeriodId).HeaderText("InspectionPeriod");
})
.Width("600px")
.Height("500px")
.Features(features =>
{
features.Updating()
.EditMode(GridEditMode.Row)
.EnableDeleteRow(true)
.EnableAddRow(true)
.ColumnSettings(settings =>
{
settings.ColumnSetting().ColumnKey(nameof(LuItemType.ItemDesc))
.EditorType(ColumnEditorType.Text).Required(true).Validation(true);
settings.ColumnSetting().ColumnKey(nameof(LuItemType.SafeWorkingLoad))
.EditorType(ColumnEditorType.Text).Required(true).Validation(true);
settings.ColumnSetting().ColumnKey(nameof(LuItemType.InspectionPeriodId))
.EditorType(ColumnEditorType.Combo)
.ComboEditorOptions(options =>
{
options.DataSourceUrl(Url.Action("GetComboData", "ItemType"))
.TextKey(nameof(LuInspectionPeriod.InspectionPeriodDesc))
.ValueKey(nameof(LuInspectionPeriod.InspectionPeriodId))
.Mode(ComboMode.DropDown);
})
.Required(true).Validation(true);
});

})
.DataSourceUrl(Url.Action("GetGridData", "ItemType"))
.DataBind()
.Render())

However, the combo isn't loaded with any data, so I'm seeing the Id of the row rather than the text description, and when I try to drop the list there's no data in it.

The data source method is as follows:

public class ItemType : LookUpController<LuItemType>
{

... SNIP ...

[ComboDataSourceAction]
public ActionResult GetComboData()
{
return View(RsContext.LuInspectionPeriod.AsQueryable());
}

}

 And the entity class looks like:

public partial class LuInspectionPeriod
{
public LuInspectionPeriod()
{
LiftingItem = new HashSet<LiftingItem>();
LuItemType = new HashSet<LuItemType>();
}

[Required]
public int InspectionPeriodId { get; set; }
[Required]
public string InspectionDesc { get; set; }
[Required]
public int? InspectionPeriodDays { get; set; }
[Required]
public int? InspectionPeriodMonths { get; set; }

public virtual ICollection<LiftingItem> LiftingItem { get; set; }
public virtual ICollection<LuItemType> LuItemType { get; set; }
}

When I click on a the cell with the combo I get this error in the console:

jquery.js:9566 GET https://localhost:44307/ItemType/GetComboData?textKey=InspectionPeriodId&valueKey=InspectionPeriodId&toLower=1&_=1492017867793 500 (Internal Server Error)

Is there anything obviously wrong with how I've set this up?