Exec, system, passthru didn't work

Hi, I tried to execute the following command from the web interface using a system call /usr/bin/play a_wave_file.wav I tried exec, system, passthru, and shell_exec. None of them worked, that is I didn't hear any sound played. Note that I'm sitting here on the server itself, and tried it with a web browser in the server. The command is executed fine when I just copy it and run it in terminal. I also made sure that nothing blocked the sound card, that is, the sound card was not in use. exec, system, passthru returns the value 2, which I don't know what it means. Any help on this will be appreciated. Thanks in advance. Reuben D. Budiardja