Having no themes active causes SQL error.

I recently installed the context module and experience the following error message when adding a new context:
user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') ORDER BY module, delta, weight, region, status' at line 1 query: SELECT module, delta, weight, region, status FROM blocks WHERE theme IN () ORDER BY module, delta, weight, region, status in C:\xampp\htdocs\Drupal6\sites\all\modules\context\context_ui\context_ui.admin.inc on line 992.

My MySQL version is 5.1.33

It cannot by an update.php issue beacuse it is the first version I use (I also uninstalled the module to reproduce the error, it was 'successful')