I uninstalled and reinstalled WP, MultiSite and BP. Everything is working now. Thanks for your help.
The problem was probably caused by one of two things:
1) I originally had installed BP first and then enabled Multi-Site.
or
2) My domain already has several “Add-on Domains” setup as subdomains on this domain. Hostgator tech support doesn’t think that will affect a Multi-Site installation with subdomains, but I’m not so sure. To be safe, I used subdirectories on this new installation.
Ok great. Thanks so much for this information. I will let you know how it goes.
Is it better to enable Multi-Site first? If I recall, I think I downloaded BuddyPress/Courseware and then I enabled Multi-Site. Maybe that was part of the problem?