Fatal error: Call to undefined function email_exists() User.php

Helo, I am using an outdated mod called wordpress united. I have managed to keep it working until the new version 3.3.1. Unfortunately, something with the new version of wordpress has created a new error for me. The mod itself is based on phpbb, but it was something with wordpress that messed it up. So, before going back to the previous version, I was just wondering if it is possible to fix it.

The main problem is that I cannot edit user’s information in wordpress. I get error after hitting edit on the uers profile page in the wordpress admin area:

Fatal error: Call to undefined function email_exists() in wordpress/wp-admin/includes/user.php on line 173

Unfortunately, I had to rename email_exists() to email_exists2() to ge the mod to work. This was not a problem with 3.2, so I am wondering what changed to create this error.

I appreciate any help. Thank you. Also, if you don’t think anything will fix it please let me know how one goes about downgrading to the previous version. Thank you.