BuddyPress.org

I got this solution from Mr. Brajesh Singh:

This is a problem with Buddypress 1.2
There are a few ways to fix this though.
In your bp-custom.php, put these lines, and it should work.

define(“BP_HOME_BLOG_SLUG”,”blog”);
function bpdev_blogs_setup_root_component() {
/* Register ‘blog’ as a root component */
bp_core_add_root_component( BP_HOME_BLOG_SLUG );
}
add_action( ‘bp_setup_root_components’, ‘bpdev_blogs_setup_root_component’ );

And to some who may not know where to put the bp-custom.php, bp-custom.php should be created in wp-content/plugins NOT in wp-content/plugins/buddypress.