Jquery Autocomplete with json fails

I am using the auto complete plugin by Devbridge and I have it all installed here is my code:

$(document).ready(function(){
    $('#request_task').autocomplete({
      serviceUrl: '<%= ajax_path %>',
      minChars:1,
      width: 300,
      delimiter: /(,|;)\s*/,
      deferRequestBy: 0, //miliseconds
      params: { artists: 'Yes' },
    });

});

This request hits my rails action and returns this json. there is only one object returned but most of the time there will be more then 1...this was just a test case:

[
    {
        "user": {
            "salt": "somthing",
            "name": "john",
            "encrypted_password": "92dadsfa6b001ffe71c3c1d8e9fb76c42d1c8afeffa739de9063d94206c",
            "created_at": "2010-09-10T14:10:54Z",
            "updated_at": "2010-09-10T14:10:54Z",
            "admin": null,
            "id": 1,
            "remember_token": "c开发者_开发百科945522b3eb0a25e36bb39155fc05b3eec301ac5e2196956f2e6f86b4b22c987",
            "email": "test@gmail.com"
        }
    }
]

I can clearly see the request in firebug but I am not getting anything for the autocomplete and it errors out...Am i missing anything...My error is

a.suggestions is undefined

I think you need to read a little further down the developers page as your response is in the wrong format:

Web page that provides data for Ajax Autocomplete, in our case autocomplete.ashx will receive GET request with querystring ?query=Li, and it must return JSON data in the following format:

{
 query:'Li',
 suggestions:['Liberia','Libyan Arab Jamahiriya','Liechtenstein','Lithuania'],
 data:['LR','LY','LI','LT']
}

Notes:

query - original query value
suggestions - comma separated array of suggested values data
(optional) - data array, that contains values for callback function when data is selected.

Sincere advice , dont construct JSON Strings. Please go for an API.
If you are using java, check this out http://www.json.org/java/
and make sure to set content-type in response as application/json

YOUR JSON is in a wrong format

Check their correct format

{
 query:'Li',
 suggestions:['Liberia','Libyan Arab Jamahiriya','Liechtenstein','Lithuania'],
 data:['LR','LY','LI','LT']
}