Won't work online with PHP 4.06

On our in house test serverrunning 4.06 this code works fine.On host server it will create the file name but will not write to it. If you create a file and upload it, it will erase everything but not write. Any Ideas why? Where should we start loking for the problem?

        <?php

                  $filename = "/path/to/file/free.txt";

                 $handle= fopen($filename,'w+');

                fputs($handle, $free);

                fclose($handle);
               ?>