Just checked if it is writable, it is and the problem is still there
I am now in the middle of an ambitious plan... I will install a clean empty forum in a sub-folder, make sure everything works, I will then start moving sections of the original database tables (posts, members, forums etc..) into the new forum database.
I will then point the original forum to the new database in config.php.
Kevin, I have already missed Mach of the Day working on this - am I wasting my time trying the latest plan?