this is in reply to the previous post that is now locked. I am waiting for additional details on the steps the user took to replicate the issue.
So far here is what I know. The user made a post in a group. He then replied to the same post and added the below link.
This time however the behavior was a little different. So long as you were logged into the site you remained logged in and could navigate anywhere except the home page and the group where the post was made. If you logged out or went to the home page you would get the error page in my previous post. You could click the back button if you just went to the home page and could continue to navigate the rest of the site except for the group.