Drupal's Batch API is a great tool for module developers to leverage when an extended task needs to be performed. The Batch API is used during Drupal's own core installation and by modules like Node Import.
Unfortunately, sometimes the default settings of PHP's mod_security extension can interfere with some implementations of Batch API.
If you're working with a module that implements the Batch API and it isn't working, there are three possible courses of action:
- Disable mod_security
- Reconfigure mod_security
- Regardless of if you do either of the first two options, you should definitely submit an issue for the module in question on Drupal.org