Index: wp-includes/ms-functions.php
===================================================================
--- wp-includes/ms-functions.php	(revision 23470)
+++ wp-includes/ms-functions.php	(working copy)
@@ -981,6 +981,7 @@
 
 	add_option( 'WPLANG', get_site_option( 'WPLANG' ) );
 	update_option( 'blog_public', (int)$meta['public'] );
+	update_option( 'rewrite_rules', array() );
 
 	if ( ! is_super_admin( $user_id ) && ! get_user_meta( $user_id, 'primary_blog', true ) )
 		update_user_meta( $user_id, 'primary_blog', $blog_id );
@@ -1977,4 +1978,4 @@
 		return min( $size, $fileupload_maxk );
 
 	return min( $size, $fileupload_maxk, get_upload_space_available() );
-}
\ No newline at end of file
+}