Attempting to change exiting user roles gives 'name already taken' Error

When attempting to edit an existing user who exists in both Drupal and vBullentin, and trying to modify user roles, upon submit, the resulting page will return the following errors:

* The name xxxx is already taken.
* The e-mail address xxx is already registered. Have you forgotten your password?

Upon disabling of the DrupalVB module I am able to make the proper edits. After re-enabling the module, I again receive the errors.