warning: preg_replace() [function.preg-replace]: Unknown modifier '|' error

When attempting to edit an existing node or creating a new node, I receive many (100+!) notifications of this error:

warning: preg_replace() [function.preg-replace]: Unknown modifier '|' in /home/mysite/public_html/sites/all/modules/pathauto/pathauto.inc on line 206.

I do not have a WYSIWYG editor installed, so it does not seem to be the exact issue addressed in http://drupal.org/node/175772 and http://drupal.org/node/121276.

I have a number of other contributed modules installed, but this error only started appearing after upgrading from 6.x-1.1 to the 6.x-1.2 version of pathauto. I've tried disabling a few other modules I thought might be conflicting, without luck. Any ideas?

Here's some more relevant info about my system:
Drupal 6.14
MySQL 5.0.81
PHP 5.2.9
Apache web server

Thanks for any and all help!