BuddyPress.org

@ikazet just to clarify .. when you say blogs in the same server, the first blog WP 2.9.1 is in http://www.siteA.com/ and the second blog is WP 2.9.2 with BP in http://www.siteB.com/ or is 2nd blog in separate folder that’s a subdirectory like http://www.siteA.com/secondWPinstall/?

If you install a second WP in subdirectory where there is also WP at root of domain, make sure that the name of subdirectory folder (or URL path) doesn’t conflict with something else in your main site at root. e.g. If you have a page in root named labs as in http://siteA.com/portfolio/ do not name the folder where you installed 2nd WP “portfolio”.