Please see http://thepaperpusher.net/forum/viewtopic.php?p=639162#p639162
for an explanation of and a workaround for this error.
But if you have repetitive strain injury and don't want to click that link for fear of bringing on joint pain:
This error is caused by overzealous application of a security subsystem in Apache that's meant to guard against a host of things, one of them being unwanted adult content. Unfortunately—
(a) the bar for such content is set quite low. A post containing the text "underage girls" can bring down the 403 hammer. ("Wait, if that's so, how come I'm seeing it in this post?" Keep reading.)
(b) configuring the security subsystem to allow such text requires high level sys admin intervention. You must have sys admin rights on the entire box, not just an account on the box.
There is, however, a workaround:
(1) identify the offending bits of text (remember, the defaults are quite prudish)
(2) once identified, interlard them with BBCodes that do not affect any letters. For example
will display as "underage girls" I realize it is a headache, but at least you will be able to post while the powers that be here try to get Gamer (or whomever) to whitelist the SFMB.
That said, WARNING!
You may find that you can preview your post, only to get hammered by the 403 Forbidden error when you submit. If you look at your BBCoded offended phrase, you'll see why: the BBCodes that did not enclose any letters were removed, and
under[b][/b]age h[i][/i]ot gi[u][/u]rls
without the prophylactic BBCode.
I recommend composing long posts outside the phpBB editor in vi or WordPad or TextEdit and copypasta the contents to the phpBB editor.
_________________"And when I fuckin' move, I slice like a fuckin' hammer."
That's just the fuckin' way it is.