I was having the exact same issue as you were experiencing. I had gone through all of the Admin's suggested tips without success. I had finally figured out that the issue was due to the following error: "The server understood the request, but is refusing to fulfill it". I proceeded to change the URL call from a HTTPS to just HTTP. This change resolved the issue. See the final code snippet below:
vargroceryDataSource = newkendo.data.DataSource({ transport: { read: { url: "http://api.everlive.com/v1/"+ apiKey + "/Groceries", dataType: "jsonp" } }, schema: { data: function(response) { returnresponse.Result; } } });