Thanks to everyone that replied with the debugging output from the wiki.
Unfortunately this debugging output also showed your password, so
PLEASE PLEASE DO NOT PASTE THE DEBUGGING OUTPUT IN A POST HERE without editing the first line at the top like so:
#0 /home/ts/towersstreet.com/wiki/includes/specials/SpecialUserlogin.php(357): User->setPassword('
YOUR_PASSWORD_IS_HERE')
But that all aside - I've implemented another few fixes, and HOPEFULLY you shouldn't even need to login to the wiki now to use it... he says
When you browse to the wiki, it should pick up your forum login automatically. If it has, you should just see your username at the top like this:
This will be in the very top right corner of your browser.
If you don't see this, try clicking on "login" again and see if it will let you login.
Again, any errors, please post them here for me.
Please make sure your password isn't being revealed in the first line of the debug error log though!.
Thanks