Getting 404 when trying to access new WPMU user account

I had my host do all the Wildcard dns settings as instructed for installing WordPress Mu. As as admin, I added myself a blog as if I were a new user. When I tried to login using the new subdomain user or try to access my profile (I’m using Buddypress plugins also) this URL:
https://bob.mydomain.com/profile

gives me a 404 error.

What is happening? The only way I can login is if I don’t use my new user subdomain (“bob” as above) and go through https://www.mydomain.com/wpmu/ and login on the admin screen, but I don’t want to do that if my “future users” would login via their own subdomains.

What’s happening here?

Thanks!