BuddyPress.org

@nahin if you want to install BP in a subsite, then add the following to your wp-config.php file (at root of your WP installation)

define ( ‘BP_ROOT_BLOG’, 3 );

change the number 3 above to the ID of subsite

@nahin Not clear what you mean. Did you try to activate BuddyPress via Network Admin > Plugins?

@nahin This happens when you have a multisite installation and you activate BuddyPress in subsite’s admin and not network-wide in Network Admin > Plugins. Is this the case with your installation?