bbPress.org

i just put in the new bbpress

it all works well apart from when i go into my posts i get this message

Fatal error: Class ‘BB_User’ not found in /home/a2583606/public_html/forum/bb-plugins/Gravatar/Gravatar.php on line 36

i hope that someone can help fix this, my forums website is http://www.forum.azcs.co.uk

thanks