[CLOSED] for submit to webservice

[odyssey]

I am in trouble to make correct call to web service. Form values are being submitted correctly the only problem is that webservice respond in xml despite that [System.Web.Script.Services.ScriptService] is uncomment, It throws an error on response. Ext.JSON.decode(): You're trying to decode an invalid JSON String:
for exampe

createNewAssets: function () {
        var frm = Ext.getCmp('frmAddNewAsset').getForm();
        frm.submit({
            url: '../../stores/assets.asmx/saveNewAssets',
            cleanRequest: true,
            json: true, //it is not working 
            params: {
                newAsset: frm.getValues(true)
            }
            success: function (form, action) {
                Ext.Msg.alert('Success', action.result.msg);
            }
        })

   [WebMethod]
    public string saveNewAssets() { 
        return "{'success' : true , 'msg' : 'Success' }" ;
    }