Getting a "This webpage has a redirect loop" on 3 out of 7 of sites created

I have multisite, buddypress, pro site - all new. I have had 5 people create sites and I have created 2 others. Everything seems to work great - although they haven't started to create their sites or they would have spotted this on their own. I tried to access their sites in the site directory. When I got this error "This webpage has a redirect loop" I then put their urls into a browser and got the same thing. Help! Thanks in advance! Linda