Try clearing your cookies just to be sure that you don't have any stragglers from when we didn't have it configured properly. You also have some domain issues if I recall - and this will be tricky because you can't share cookies between two domains. I'll be glad to take a look, but to share a common login between your galleries and forums, you will need to use the same domain name - this is a cookie limitation, not a PhotoPost limitation.
The alternative is that users will have to login to both sites.
To clear your cookies, you can link to:
and erase your cookies.
Please do not PM me for support or sales questions. Thank you for your understanding.