How to fix this error in drupal: ajax: ajax.form.ajaxSubmit is not a function I am creating a form with ajax submission in my Drupal custom form module. 

When I click my submit button, I get the following error:


  ajax: ajax.form.ajaxSubmit is not a function.


I am searching some blogs, try something like uninstalling lightbox2 module, color box module, etc. But again the same error is displayed.

How can fix this error?

Note: I installed Lightbox first, but after this error I uninstalled it again.
You'll need to include the Drupal ajax drupal_add_library('system', 'drupal.ajax');