Log-In problems

I always log-in with the quick log-in feature on the forums. Then it tells me my log-in was successful. But then when I go to rate an album, it tells me this:

 

As a registered member (register here if not), you can post rating/reviews (& edit later), comments reviews and submit new albums. You are not logged, please complete authentication before continuing (use forum credentials).

And then I have to log in here again: http://www.progarchives.com/forum/login_user.asp

 What gives?

I have been having this kid of problem for few years now... my second login - the one required to write reviews - does not work, no matter how many times I re-enter my "forum credentials" when asked.
This is really frustrating since, as an old member, I simply cannot continue with my contributions to the PA.
My guess is that this problem occurred around the time when I switched from PC to Mac. From  another computer at my then working place, I was able to write and submit, but it was a PC machine, but from my home Mac - nope! Unfortunately, I have never received a satisfactory advice from the Admin here, what should I do? Is it only me and my MAC? There must be many more Mac users by now here too...?