BuddyPress.org

The words “DNS error” do not appear in WPMU or BP, so that error is not to do with WPMU or BP. That is going to be host configuration. You need to check with your host to see if you have wildcard subdomains enabled.

Other places to look would be your Apache (or webserver) error log, to see if Apache even sees the request on a subdomain. Or if you have too many redirects for some reason, this would be flagged up here too.

Another thought is maybe you have an existing or apache.conf master rule which is re-writing the domains before the WPMU htaccess is read.

And, that’s what the problem is – it’s not BP not working, it is WPMU not working. Obviously WPMU has to be working 100% for BP to work.