Already a group member but locked out??

I've never had this problem before, where I am getting notifications that people are positing to group's walls that I am a member of, but when I go to check them it brings me to the page where everyone's pictures are listed that are currently in the group, and it gives me the option to "Join Group," as if I am not a member. However, when I click that, it says I'm already a member.
I think this is because I was a member of these groups before I deleted my Facebook (for abt a month) and when I came back it did not register that my account was reactivated??
Any thoughts/tips?

Try changing the URL from '[You must be registered and logged in to see this link.].facebook.com....' to '[You must be registered and logged in to see this link.].facebook.com...'. That should show whether you're connected to the group or not.