BuddyPress.org

First, if you are creating sub domains for each individual blog make sure the blogs are being confirmed through the submitted email during registration. you will see a white screen for every blog not confirmed.

If you are setting up WPMU with subdomain blogs then you have to add a wildcard DNS record on your server. If you do not, you’ll have significant issues. This is detailed in the readme.txt file that comes with the WPMU install package.

This is why we ask everyone having issues with BP if they fully tested WPMU and made sure it was functioning properly before installing ANY plugins–including BuddyPress. Fully testing does not mean giving it a cursory once over. It means fully testing all the major functions. This should take some time. The most obvious first function to test is the creation of additional blogs.