fatal error in newly installed Membership plugin

dear person,

i have wp 3.4.1

have just tried to install Membership via the WPMU dashboard and get a fatal error:

Fatal error: Call to undefined method stdClass::set_help_sidebar() in /home/willdo/public_html/tbdev/wp-content/plugins/membership/membershipincludes/classes/class.help.php on line 73

Any ideas?

thanks,

William