I think Graig pinpointed the issue when he mentioned getting the Headers already sent error.
I think the Headers Already sent error is occurring in the menu.php file when the flash object tries to call it due to the following lines:
Just to test this theory, try removing those lines from the menu.php file.
Most of that is just to prevent caching. another tack to prevent caching is to append a random number as a query string when calling the menu.php file
In php, I would do that as:
<a href="menu.php?rand=<?php echo rand(); ?>">Link</a>
not quite sure how that would work in Flash though.