multisite with buddypress

I first tried asking this on the Buddypress forum – but have not received any suggestions . . .

I need to designate a subsite as root blog. I have found 2 answers in codex by either adding:
define ( ‘BP_ROOT_BLOG’, 2);
in wp-config.php or in bp-custom.php files. I’ve tried both methods and in both cases get the same error:

Fatal error: Call to a member function get() on a non-object in /public_html/wp-includes/query.php on line 27

I have WP 3.3.1 and BP 1.5.3.1 installed.