I have installed following modules :

jQuery Update 7.x-2.2 Updates jQuery to jQuery 1.5.2 and jQuery UI 1.8.11
jQuery plugins 7.x-1.0 An API and home for miscellaneous jQuery plugins.
References 7.x-2.0-beta3
User Reference 7.x-2.0-beta3

I have added user reference field to the blog.

For Custom form validation, I have used drupal_add_library('jquery_plugin', 'validate');
Everything works fine on custom form validation.

However, On user reference auto complete I am getting following errors:

Alert Message
-------------

An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: http://localhost:8888/DRUPAL7_9/user_reference/autocomplete/node/blog/fi...
StatusText: parsererror
ResponseText: {"user2 [uid:2]":"\u003cdiv class=\"reference-autocomplete\"\u003euser2\u003c\/div\u003e"}

Firebug Message
---------------
invalid label
{"user2 [uid:2]":"\u003cdiv class=\"re...mplete\"\u003euser2\u003c\/div\u003e"}

Please help me.