reply on phpbb3 forum

For what it's worth, I'm a moderator at a site that switched over to phpBB3 and Safari won't allow users to post either. And it's JUST Safari. IE works, Firefox works, Konqueror works (which I found odd, since Safari and Konqueror are built on the same engine), Opera works. Heck, even Opera mobile works. The site is http://www.gamersliberationfront.com/ Any time someone tries to post or reply with Safari, they get an error 400 "Bad request."

Bad Request

Your browser sent a request that this server could not understand.
Apache/2.2.0 (Fedora) Server at www.capricorngraphics.com Port 80

I've duplicated this problem (Unable to login or reply) on phpbb3 forums using Safari on a Windows XP.

The default cookie setting is for 'Only to sites I navigate to'. You can never login via phpbb3 because it redirects immediately upon login and sets a new session id. (Which means, you're not navigating to the site after login submission, the server is forcing your browser to navigate to a new page and set an updated cookie at the same time).

Try changing your cookie settings to 'Always', then clear the domain cookies, browse a page or two, then try to login again. I think it'll work for you.
Cheers.