Pages only load when logged in!

I have seven wordpress blogs on my server, and am getting the same problem for a lot of them. The pages only load when I am logged in. Otherwise, it creates a blank page, but not a 404.

Strange part 1: Upgrading versions worked in some cases, but others it didn’t. Some blogs are working with older versions of WP.

Strange part 2: I use the SEO Title plugin. When turned on, the title works, otherwise it doesn’t. In general, plugin codes runs.

– I tried turning the plugins off
– Changing themes doesn’t work, same problem
– Admin pages load fine
– Upgrading WordPress worked in some cases, but not all

Could it be a SQL issue? Please help.