Hi,
Just to double check for myself, did you use the upper right fields to log into the archive? The center login fields only work once, at activation, and part of the process includes logging out and logging back in again using the upper right fields.
I also recommend logging out of the archive, and then closing and restarting your browser before logging in again.
Being logged in to the forum is not required to post to the archive, and in fact, you are still validating for forum membership. Please check your email for the activation link.
Hopefully the browser restart will help to clear the issue. Please let us know if the issue persists, and we'll get it sorted out.