I can't answer the question on the normal website, but I maybe able to assist with the phpBB forum. I had the same problem with a forum I ran where one member couldn't access the forum at all and just kept getting the 404, it was fixed by using a modification to your phpBB board called "Auto Cookies MOD". Unluckily phpBB is down at the moment so I wasn't able to get the link to the mod, but just do a search on the forum when it is online again.