Index: bp-themes/bp-default/functions.php
===================================================================
--- bp-themes/bp-default/functions.php	(revision 3022)
+++ bp-themes/bp-default/functions.php	(working copy)
@@ -128,6 +128,16 @@
 }
 add_action( 'pre_get_posts', 'bp_dtheme_fix_get_posts_on_activity_front' );
 
+/* WP 3.0 requires there to be a non-null post in the posts array */
+function bp_dtheme_fix_the_posts_on_activity_front($posts, $wp_query) {
+	// NOTE: the double quotes around '"activity"' are thanks to our previous function bp_dtheme_fix_get_posts_on_activity_front()
+	if ( empty($posts) && !empty($wp_query->query_vars['page_id']) && '"activity"' == $wp_query->query_vars['page_id'] )
+		$posts = array( (object) array( 'ID' => 'activity' ) );
+	
+	return $posts;
+}
+add_action( 'the_posts', 'bp_dtheme_fix_the_posts_on_activity_front', 10, 2 );
+
 /****
  * Custom header image support. You can remove this entirely in a child theme by adding this line
  * to your functions.php: define( 'BP_DTHEME_DISABLE_CUSTOM_HEADER', true );