Enabling module breaks Permissions page

Hi! The reftagger module works as expected and is very useful, thanks!
However, when the module is enabled, the drupal permissions page doesn't load up, and it gives this error:

Fatal error: Unsupported operand types in ...../drupal/modules/user/user.admin.inc on line 696

It seems data is being passed to the permissions module in a way which it doesn't expect.