dhtmlXCombo is not defined

I am Using Combo_box module in drupal 7.16. I am getting the error like “dhtmlXCombo is not defined”… I just created a combobox field type. When ever i load that page,i get this error. May i know what is the issue…? and one more need… Any suggestions about how to pass an ajax request when i select value…?

There is few information.
Please, provide completed demo to test it.
docs.dhtmlx.com/doku.php?id=othe … leted_demo