Warning: preg_replace error: Empty regular expression alinks.module on line 188

After creating the first term and navigating to a page that contains it, the page throws this error:

warning: preg_replace() [function.preg-replace]: Empty regular expression in /home/swwbwei5/public_html/sites/all/modules/alinks/alinks.module on line 188.

The term was a single word, and I used case insensitivity with it as I want to ensure any version of its spelling is turned into a link. I searched for this error elsewhere and can't find the same issue documented so far.

Drupal 5.21, PHP 5.2.6, MySQL database 5.0.89