I login but get logged out

I login and am taken to the Login Welcome Page, but as soon as I surf around the site and come back to the Login Welcome Page, I get sent to the Membership Options Page as a visitor.

The problem may be that you're mixing the use of the www subdomain in your links: example.com vs. www.example.com. They're not the same site for the login session.

When a user logs in under example.com, he's logged into the site without the www, but if then your menu links point to www.example.com, it's like taking him to a different site where he's not logged in.

Web browsers treat those two as entirely different domains, so when you try to visit a protected page with the www URL when you logged into the URL without it, you're not logged in and get redirected to the Membership Options Page if you try to access protected content. It's like being a visitor instead of a paying member.

Please see this article for more information:
http://s2member.com/kb-article/how-to-avoid-login-issues/

Your menu links may be using the www while your site doesn't, and that's what's causing the problem. A user logs in at the non-www version of the URL and then, once they click one of the menu items, are now considered "not logged in".

Please update all your links to the version your WordPress installation uses.