Errorcallback - how to return back the error in correct json format

arunsharma

I am using from salesforce

In the ajax :

ajax: function ( method, url, data, successCallback, errorCallback ) {

if ((mType === 'Hot') && moperation ==='Delete')
{
alert('this cannot be deleted ');
return errorCallback( {"error": "this record cannot be deleted"} );

                        }

}

I am getting the system error occurred as I think the json is not correct . what is the right format .