For some reason the ahah functionality stopped working after a theme upgrade. I tried the simplest examples of ahah and it doesn't work. I also downloaded ahah-helper module, and even the example there doesn't work.
I copied exactly every code that's in this link : http://drupalsn.com/learn-drupal/drupal-tutorials/getting-going-ahah-and-drupal-6
when I submit a ahah form - the page loads again without any other affects (the form doesn't really gets submitted, form_submit not invoked).
i have no idea where to start looking for a solution....
I'm using drupal 6.
This is happening because you have a second version of jquery loaded by your theme. This is either causing a conflict between jquery versions or introducing a jquery library that is incompatible with Drupal's core js.
As far as I'm aware the latest version of jquery that works with Drupal 6 is 1.3.2, which you can install using the jQuery update module. I've read reports of people getting v1.4 and even v1.5 to work but at the cost of some core functionality like AHAH