Introduction to XML in Flash
       by senocular

Trouble With Raw Post Data In PHP
So the Flash XML methods send and sendAndLoad send your XML to a URL as raw Post data. The variable commonly used to access this post data in PHP is:

$HTTP_RAW_POST_DATA

Sometimes this doesn't always work (or your version of PHP may not support it). If you're having problems using $HTTP_RAW_POST_DATA, try instead using

file_get_contents("php://input");

php://input represents the standard input stream of the PHP file. Not only does the above solution use less memory than $HTTP_RAW_POST_DATA, but it also does not require any special php.ini directives to function properly (which may be causing you problems with $HTTP_RAW_POST_DATA in the first place). For versions of PHP >= 4.3.0.