Getting AJAX Error when handling ajax request in hook_form_alter where form element has #element_validate that comes from a them

Have you checked that the ajax callback is even initializing the theme at all? That's not guaranteed.

This needs a test module or ideally a test case.

This is not a drupal core bug.

You will need to require_once() the file in which alpha_theme_settings_validate_not_empty() is defined.

Can you make a super-simple demonstration module that demonstrates the simplest case and put it in a sandbox? I'll try to take a look at it. I'd prefer you demonstrate this with a core theme, but since it seems to require the theme to be altering... (BTW, the module sandbox you linked to above doesn't seem to work. Did you promote it?)

Hi there,
I'm having the same thing: I'm trying to add some ajax powered form settings to an Omega subtheme.
So in theme-settings.php of my subtheme I call hook_form_system_theme_settings_alter() and have a select field with #ajax and callback. (Trying to update some fields according to a preset that can be selected with the ajax-calling select field). Getting the exact same error...

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Same problem here. Trying to add a managed file field to my theme-settings.php. Theme is I subtheme of Omega. The files do get uploaded and the file_managed stores correct data.

Error message:
ResponseText: Fatal error: Call to undefined function alpha_theme_settings_validate_not_empty() in
/includes/form.inc on line 1379

Same issue occurs if a form is in an include file, as is the validate function, and that module's .info file doesn't reference the include file and another module comes along and adds #ajax to another form element.

Support requests are never major or critical.

Try using
http://api.drupal.org/api/drupal/includes!form.inc/function/form_load_in...

I'm totally stuck due to this problem. I'm looking for a solution.
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Why doesn't anyone care about this issue?

I have the same issue today with Search configuration module, when I created a custom button with #ajax handler. The solution described on #17 comment it's works.

Example:

    //check if module with #element_validate callback on hook_form_alter is enabled
    if(modules_exists('something_module')){

          //Include file with #element_validate callback using this function, instead of module_load_include()
          form_load_include($form_state, 'inc', 'something_module','something_module.admin');
    }

However, include file for execute the callback that will not used, it's strange. So, a created a simple patch with a simple test:

  //file form.inc on _form_validate() function on lines 1411 e 1412
  if(function_exists($function))
            $function($elements, $form_state, $form_state['complete form']);

For apply the patch, use git am command.