I created two threads here and here about that internet explorer works in quirks mode and that broke the layout. After a bit of investigation I found that somehow php make s
If a browser is treating the two pages differently, then there's some difference between them, even if it's not immediately apparent when you "View Source".
I recommend using a tool such as Fiddler to look at the actual page content as delivered from the server.
Edit: You'll find that the "RAW" and "HEX" tabs are more important than "TextView". Start with "Raw" and compare the "Content-Length" header, then look at "HexView" to see what has changed.
Most likely there is some output going to the browser before the doctype.
Ensure that:
<?php
opening tags...in any of the files that are being parsed to generate your output.