Ember data help! Unable to de-serialise JSON to model

I'm using:

Ember 1.10.0 Ember Data 1.0.0-beta.15

I have a model like this:

//models//acceptedtask.js
import DS from "ember-data";
export default DS.Model.extend({
    userAggregateId: DS.attr('number'),
    taskAggregateId: DS.attr('number'),
    name: DS.attr('string')
});

I get this back from the server:

{"acceptedTask":{"id":5,"userAggregateId":1,"taskAggregateId":3,"name":"Clean table"}}

Whenever I get this json back ember throws the following error:

Error: Assertion Failed: You must include an `id` for task-management@model:acceptedtask: in an object passed to `push`
    at new Error (native)
    at Error.EmberError (http://localhost:4200/assets/vendor.js:22992:23)
    at Object.Ember.assert (http://localhost:4200/assets/vendor.js:14489:15)
    at Ember.Object.extend.push (http://localhost:4200/assets/vendor.js:74317:15)
    at http://localhost:4200/assets/vendor.js:74783:24
    at Object.Backburner.run (http://localhost:4200/assets/vendor.js:10749:27)
    at ember$data$lib$system$store$$_adapterRun (http://localhost:4200/assets/vendor.js:74759:32)
    at http://localhost:4200/assets/vendor.js:74780:16
    at tryCatch (http://localhost:4200/assets/vendor.js:60990:16)
    at invokeCallback (http://localhost:4200/assets/vendor.js:61002:17)

Is anyone able to help me with this? I feel like I'm missing something basic after trolling half the internet for similar problems :(

Thanks,

Tom