Register tab not visible

I have installed WP and the BP plug-in, and activated the default BP theme. I have added a few new pages that all show up as tabs on my site. I have enabled the automatic generation of directories as they are listed in BP installation.

When I select the “Allow anyone to register” checkbox in Settings/General, I do not get the “Register” tab that is shown in the WPMU documentation.

What am I doing wrong?