i had that same problem once i made a ticket here (old site like 8 month ago) and sent my code file i was missing on the top of the site this
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
check that out and try again :)