Exception: theme() may not be called until all modules are loaded. in theme()

I am getting this when I try to use simpletest in D8:

An AJAX HTTP error occurred. HTTP Result Code: 500 Debugging information follows. Path: .../drupal/batch?id=29&op=do StatusText: Service unavailable (with message) ResponseText: Exception: theme() may not be called until all modules are loaded. in theme() (line 964 of .../drupal/core/includes/theme.inc).

I get this same error as well. Mostly when trying to run simpletests on D8 against Bootstrap or Batch API.

Just a head's up for anyone who ran into this error message by changing a module. Make sure you don't break some array code by using a semi-colon instead of a comma at the end of your last array value e.g

array(
"foo" => "foo data",
"bar" => "bar data";
);

Make sure your last element looks like

"bar" => "bar data",

I'm using Version 7.16

if you did't get any solution then goto the theme.inc file and comment this line
//throw new Exception(t('theme() may not be called until all modules are loaded.'));
now it's working fine...

This also crashes the CiviCRM mail-send cronjob.
(Drupal 7.30; CiviCRM 4.2)
I get:

Exception: theme() may not be called until all modules are loaded. in theme() 
(line 1017 of /home/xxx/public_html/includes/theme.inc).

and after trying #6, I still get

PHP Fatal error:  Call to undefined function _system_default_theme_features() in 
/home/xxx/public_html/includes/theme.inc on line 1423

This queue is not for support requests. Please open a support request in the appropriate forum.

Is there a way for me to have this be just a regular drupal erorr and not something that completely stops my site.
How do I get rid of it once it happens?

Ask in the forums for support.

To file a bug report, you first need to check you can reproduce it on a fresh installation, and report what you were doing when getting the error message. I did it, and I cannot reproduce this bug. I doubt it's a Drupal core bug, since Drupal doesn't call theme() when its bootstrap phase is not completed.

  // If called before all modules are loaded, we do not necessarily have a full
  // theme registry to work with, and therefore cannot process the theme
  // request properly. See also _theme_load_registry().
  if (!module_load_all(NULL) && !defined('MAINTENANCE_MODE')) {
    throw new Exception(t('theme() may not be called until all modules are loaded.'));
  }

Check also your site is not in maintenance mode.