Okay, so I found the error. It was an error in the deploy script.
IE6 gets a different script to everyone else (grumble). I’d managed to make a typo in the deploy script that caused the following line to embed itself in the script:
//}();/* Copyright (c) 2007, Katharine Berry
Instead, it should have either been omitted or read as follows:
//}();
/* Copyright (c) 2007, Katharine Berry
Unsurprisingly, there was a syntax error on the line immediately following this one. The typo causing this has been fixed.
As an added bonus, you can now log in simply by hitting return. This will serve as an interim fix for those whose screens are too narrow for the login screen to fit until I come up with an implement a better solution. Also it’s generally easier.
Note that IE6 still occasionally hangs on “Precaching…”
This is caused by the mapapi failing to load, and can generally be fixed by reloading the page. It’s horribly inconsistent. As are many IE6 issues. 
