bartoli I had a similar problem. It was related to the site's daylight saving timezone correction code. The site has a record of my computer's timezone setting. When the timezone has changed on my computer, the site tries to re-direct to the profile page. But it has the wrong URL.
I fixed my problem by going to:
http://www.aquaticplantcentral.com/forumapc/profile.php
Then click on "Edit Options". Towards the bottom of that page is the timezone setting. Change that to the one currently used by my computer. Then click on "Save Changes". That fixed my problem.
Hope that helps.