So I've been having this issue as well. I found a little workaround though that seems to be working pretty consistently for me.
Recently Kroger announced their new portal feed.kroger.com which I believe is intended to replace greatpeople.me eventually.
Well through this portal, I'm able to get to my expressHR (where you can see your paystubs and other information). Once I get to expressHR I am then able to, look at my pay stubs if I feel the need to, and log out of expressHR. Once I hit the logout button it asks if I want to log out of all siteminder sites which doing so seems to do the trick for me. Sometimes when trying to get to greatpeople.me it'll give me the message but one or two refreshes tend to fix let me through.