Feed import breaks due to ajax error When I tried to do a feed import, I got the following error.

An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /batch?id=1726&amp;op=do
StatusText: OK
ResponseText [Omitted text]

(There are quite a few similar errors on the web, for example https://www.drupal.org/node/1125060.)
When I changed the author field to 'site-admin' (see attached image), auto-complete seems running and popup the following error.

An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: http://site-prod.local/user/autocomplete
StatusText: OK
ResponseText: my_site_name | my_username
[url1]
[url2]
[url3]
[Search form]
[Primary tab: View (active tab)]
[Edit]
[Shortcuts]
[Broken links]
[Devel output]
[My username]
[Email]
[Omitted text]

The log message is the following.

Warning: Cannot modify header information - headers already sent by (output started at /var/aegir/platforms/production/drupal-7.27/includes/common.inc:2700) in drupal_goto() (line 703 of /var/aegir/platforms/production/drupal-7.27/includes/common.inc).

If I put exit() right after drupal_json_output(). The related problem seems resolving itself.
When I run drush -d -v search-index, the indexing stuck at around 61%. This indicates some problems with a node.
By using xdebug and vdebug (plugin for vim), I am able to step into the code and ping point the issue.

In https://api.drupal.org/api/drupal/includes!common.inc/function/drupal_cron_run/7

I put a watchdog: watchdog('bug_cron', '&lt;pre&gt;'. print_r($module, true). '&lt;/pre&gt;'); inside.

// Iterate through the modules calling their cron handlers (if any):
foreach (module_implements('cron') as $module) {
      // Do not let an exception thrown by one module disturb another.
      try {
        // NOTE: put a watchdog and look at your log message. 
        // You should able to see which module causes issues.
        watchdog('bug_cron', '&lt;pre&gt;'. print_r($module, true). '&lt;/pre&gt;');


        module_invoke($module, 'cron');
      }
      catch (Exception $e) {
        watchdog_exception('cron', $e);
      }
    }


It is the search module causes issues. Disable it, then uninstall the setting via the drupal menu GUI, then it is fixed, but I am not sure why search module causes issues.

Updated at 2015-05-26

It turns out my module uses hook_url_inbound_alter + drupal_goto caused issues. It is not easy to debug, because there are couple of side effects.