Im not familiar with buddypress – someone else asked about this as well, but I think because of the social networking integration, some of the native wordpress user registration features are disabled. I’m not exactly sure of this.
My plugin works ONLY on the WordPress-provided user registration hooks.
Once active, any user who registers will have their IP address stored in the “website” field.
Go to “Users”, click the user (as if you were going to edit the user), then scroll down to website. The IP address from which they registered will be listed as https://1.2.3.4
(1.2.3.4 is a generic example of the IP address)
You can then block just that user by adding 1.2.3.4 to the Discussion Comments Blacklist (under settings), or the whole subnet by adding 1.2.3.
Please let me know if this helps.
Thanks in advance,
-JP