That sounds like a wordpress login session issue, not an s2 access restriction. When you are asked to login, is that on your s2 Membership Options Page? what do the variables say in the URL after the question mark?
If you’re logged in as admin, you wouldn’t be restricted or redirected there by s2Member. So it does sound like a login session issue.
Make sure you’re not mixing the use of www and without in the links on your site, those are considered separate sites, so if you login without and then go to the www, you won’t be logged in there.
There could be other reasons, though, like a browser cookies or caching thing…
I suggest you google getting logged out from wordpress, or wordpress login session problems, and see what you can find to help troubleshoot it.
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