I\'ve got a new site we\'re working that uses HTML5. Everything validates except for the LESS stylesheets and the Facebook tags. However, Chrome will not autofill properly.
Sorry I can't give you a definitive answer, but I would start with removing everything from the page except that input field. If it works then I would start "binary search" - remove half of the original layout and see if it works, if it isn't - remove another half of what's left and so on, until problem line is found.
Same could be applied to css, js, etc. It is a pretty effective way of searching for errors (for 1024 lines of code you will find exact problem line in just 10 steps).