Functions not available when run as Scheduled Task?

Don't laugh but we have a Win 2003 Server set up with WAMP, and the PHP/MySQL scripts work great. I set one up to run as a scheduled task: C:\php5\php.exe "D:\wamp\www\scriptname.php" ...but nothing happens and the Scheduled Tasks log says that it exited with an (ff). So I entered the above manually into a command prompt, and it said that mysql_connect() is an unknown function! WTF? It's like it's trying to use a different php.ini file that maybe has mysql commented out. I double checked that all the php.ini files on the machine do have mysql enabled, and anyway mysql works fine normally. Anyone know what PHP is doing to me here in the scheduled service?