BCS - Security. Epic Fail

Well, attempting to log on to the "New British Computer Society" site, this morning (Ed notes: what happened to the perfectly acceptable old BCS and how much did that new logo cost?), I was presented with this rather over-informative error:

exception 'AmaxusSecurityException' with message 'Invalid token for request' in /mnt/amaxus4/private/inc/controller/Frontend/FrontendController.class.php:157
Stack trace:
#0 /mnt/amaxus4/private/inc/controller/Frontend/FrontendController.class.php(131): FrontendController->checkRequestToken()
#1 /mnt/amaxus4/private/inc/class/common/Controller.class.php(678): FrontendController->runAction('login')
#2 /mnt/amaxus4/private/inc/class/common/ControllerDispatcher.class.php(68): Controller->handleRequest()
#3 /mnt/amaxus4/private/inc/class/common/ControllerDispatcher.class.php(56): ControllerDispatcher->handleRequest(Object(UserController))
#4 /mnt/amaxus4/site/_server.php(92): ControllerDispatcher->dispatch(Object(ClientRequest))
#5 {main}

Not very good at all for the: