Have dug further and it is something to do with the way the file is created. I am using Notepad - if I "save as" and rename, the new copy works fine in both IE9 and Chrome. Running a hex compare using Beyond Compare says they are both identical - but one works and the other doesn't? I can't see a way to spot what encoding the file is in - but if I save as utf-8 the file is different (first 3 bytes) - so I assume all versions I have created are ANSI encoded as that seems to be the default. However that doesn't explain why the original file will not load correctly and the new one does - maybe I just got unlucky but I don't like not understanding... Is UTF-8 a requirement for HTML?