Module works, but anonymous users get blank pages

I have two separate Drupal sites (with the possibility of more to come), and wanted to use SSO to both allow single sign on and also allow me to consolidate the registered user list. I successfully set up a shared database, with site-specific and shared tables as indicated. All seemed to be going fine, until I realized that visitors to the sites who were not already signed in were seeing a completely blank page. (I typically left myself signed in.) I confirmed this by logging out of both sites, refreshing the page, and being unable to view any normal content. (If I went back in my history and found an admin page, I was able to bring it up, where it said I was not authorized, and I was able to successfully log in and make changes.)

I turned off the singlesignon module in both sites, and now the sites are functioning normally again. This is OK for now, since I still have the shared tables and the single user list. I'd really like the single sign on functionality, though, and I also want to make sure that turning off the module won't cause any problems with the database. Any help appreciated. Thanks!