When osascript
runs from PHP, through the web server, it's not running with a login context, so it can't send Apple events to applications running on the desktop (like the Finder). You'll find that a similar issue arises if you try to use osascript
over SSH.
Login contexts are a complex, poorly documented area of OS X. You may want to get your hands on a copy of Amit Singh's Mac OS X Internals: A Systems Approach if you want to learn more about them.
If you don't, though, the answer is generally pretty simple: don't depend on osascript
working correctly from the web server.