Ultimate Facebook plugin triggered a fatal error

Hi! I downloaded and installed Ultimate Facebook following the instructions and saw the below message when I tried to activate it:
"Plugin could not be activated because it triggered a fatal error.

Fatal error: Cannot redeclare class FacebookApiException in /home/wheelofcommerce/hotaphrodite.com/wp-content/plugins/wpmu-dev-facebook/lib/external/base_facebook.php on line 107"

How do I fix it?

Thanks!