Can't Change Layout

[Cassie]

I've been using the old layout for a few months but now I want to revert back to the new layout for a while, but when I try, I get a huuuuuge page full of nonsense, codes and symbols etc like this;

<removed as it gives away information I'd rather the world not see  >

Is this just my computer, orrr....? 'Cause I really want to change my layout now. Just thought I'd let you know in case it's happening for other people too.