Register_shutdown_function does not work

Hi ! I'm downloading a file via ftp to my server. The file should be destroyed IN ALL CASES when then script ends - but it isn't. Have a look at the following code-snippet. I register "OnShutdown" as a Shutdown-Function, but the filename isn't unlinked when the script terminates. Calling OnShutdown directly deletes the file (just as a "debug-test"). Any ideas, why OnShutdown isn't called when the script terminates ? Martin <?php register_shutdown_function("OnShutdown"); $tmp_filename = ""; // Temp Filename on server function OnShutdown() { global $tmp_filename; if ($tmp_filename != "") { unlink($tmp_filename); $tmp_filename = ""; } } class Download {... class to download file }; ?>