BuddyPress.org

@fugu78,

you are using joomla on the mainsite and WordPress on the subdomain.
Question is: is WP sharing the same DB as joomla or have you a complete separate install (db & cms) for your WP/BP site ?
Which type of WP install do you use ? Single or network ? (more about)
Are mainsite users and wp site users the same people ?

BuddyBoss has his own support forum. You probably have better to ask there directly.