Flex app no longer able to POST byte data to .php file. Could this be solved with PHP server configuration?

Question

I have developed a program in flex 4.5 which creates byte data (the byte data is consumed by a larger, separate program and not part of this issue). In order to capture the byte data and write to actual .bda files, I am using flash.net.URLLoader to POST the bytedata through a flash.net.URLRequest to a .php file that captures the data and writes it to the server.

This process has worked like a charm until recently (possibly as a result of a PHP upgrade on the server or configuration change). Only the two largest files (about 1 MB a piece) are NOT being written to the server and I believe that the .php file is not being called for these two files at all.

What could be causing this discontinued function... any ideas?

The AS3 code in Flex 4.5:

        var byteArrayOut:URLRequest = new URLRequest('byteDataCatcher.php?filename=' + filename + '.bda');
        byteArrayOut.data = dataByteArray;
        byteArrayOut.method = URLRequestMethod.POST;

        var byteArrayOutLoader:URLLoader = new URLLoader();
        byteArrayOutLoader.dataFormat = URLLoaderDataFormat.BINARY;
        byteArrayOutLoader.load(byteArrayOut);
        byteArrayOutLoader.addEventListener(IOErrorEvent.IO_ERROR, failedToWriteBDAFile);

The PHP code ('byteDataCatcher.php'):

$data = file_get_contents("php://input");

$filename = $_GET['filename'];//"byteData.bda";

file_put_contents($filename, $data);