Model:

public class Product
{
public int ProductID { get; set; }
public string Name { get; set; }
public string ProductNumber { get; set; }

public List<ProductLocations> Locations { get; set; }
}

public class ProductLocations
{
public string Address { get; set; }
}

Controller 

[GridDataSourceAction]
[HttpPost]
public ActionResult PostDataMethod3(Product Param1, string Param2, string Param3)
{
try
{
List<Product> products = new List<Product>();

products.Add(new Product { ProductID = 1, Name = "Product 1", ProductNumber = "12345" });
products.Add(new Product { ProductID = 2, Name = "Product 2", ProductNumber = "12346" });
products.Add(new Product { ProductID = 3, Name = "Product 3", ProductNumber = "12347" });
products.Add(new Product { ProductID = 4, Name = "Product 4", ProductNumber = "12348" });
products.Add(new Product { ProductID = 5, Name = "Product 5", ProductNumber = "12349" });

return View(products.AsQueryable());
}
catch (Exception ex)
{
string error = ex.Message;
return null;
}

}

AJAX call

var appJson = {
"Param1": { "ProductID": 1, "Name": "test product", "ProductNumber": "P123", "Locations": [{ "Address": "Address1" }, { "Address": "Address2" }]}, "Param2": "Param2", "Param3": "Param3" };

$('#postData3').click(function (e) {
e.preventDefault();

$.ajax({
url: '@(Url.Action("PostDataMethod3"))',
type: 'POST',
traditional: true,
contentType: "application/json",
dataType: "json",
data: JSON.stringify(appJson),
success: function (response) {
alert('Succcess');
$('#grid').igGrid({ dataSource: response }).igGrid("dataBind");
},
error: function (xhr, ajaxOptions, thrownError) {
alert('Failure - ' + xhr.responseText);
$('#grid').igGrid({ dataSource: null }).igGrid("dataBind");
}
});
});

Eroor:

2022infragisticerror.igGridQueryStringToJson.zip