Uncaught SyntaxError: Unexpected number in kendo ui - json

Question

I have kendo ui popup which sends a request to an action method. The action method returns json and then my code breaks in the kendo.all.min.js file and the error method says Uncaught SyntaxError: Unexpected number
My kendo code below:-
var cloudStore = new kendo.data.DataSource({
//batch: true,
pageSize: 25,
transport: {
create: {
url: "/Admin/AddCloudStore", //(/ControllerName/ActionName)
type: "POST"
},
update: {
url: "/Admin/UpdateCloudStore",
type: "POST"
},
parameterMap: function (data, operation) {
console.table(data);
var result = {};
// For update and create send the entire object
if (operation === "update" || operation === "create") {
return data;
//return JSON.stringify({ service: data });
}
return null;
}
},
schema: {
model: cloudStoreModel,
errors: "error"
},
error: function (e) {
console.log(e);
}
});
Am I suppose to return something else from the action? Any help on the issue would be appreciated
Edit: Okay seems like the problem is with what I am return from my .net action method. Adding my action method below:-
public ActionResult AddCloudStore(DataAccess.Model.domain_config_cloud store)
{
try
{
using (var context = new DataAccess.Model.CondadoMediaVault())
{
if (store.cld_cmp_key <= 0) store.cld_cmp_key = Session["sel_domain_key"].ConvertToLong();
var list = context.domain_config_cloud.Where(x => x.cld_cmp_key == store.cld_cmp_key && x.cld_is_active && x.cld_category == "primary").ToList();
if (list.Count > 0)
return Json("There is already a primary cloud store."); //returning string
long user_key = 0;
long.TryParse(Convert.ToString(Session["user"]), out user_key);
var maxKey = context.domain_config_cloud.OrderByDescending(x => x.cld_key).FirstOrDefault();
if (maxKey == null || maxKey.cld_key == 0)
return Json("Error"); //returning string
else
store.cld_key = maxKey.cld_key + 1;
context.domain_config_cloud.Add(store);
context.SaveChanges();
}
}
catch (Exception ex)
{
MediaVault.BLL.ErrorLoggging.DbExceptionLog.LogError(ex);
}
return Json(store); //returning object
}
So the kendo ui code breaks when a string is returned from the action method. If an object is returned the code does not break. What is the exact return type which is expected by kendo ui?