ACL = Access Control List aka user permissions in the Windows world.
So you're running IIS... And then you're getting a 403.1 error which means that "execute" was not allowed. I'm gonna take a wild guess and say that this is your own server as you said you were missing a .dll and had to find it (a hosting company would have done this themselves). So it comes back to how you configured your site on your IIS.
If you have access to the Windows server, go to the Internet Services Manager, select your site, select "Properties", go to the "Home Directory" tab, and check "[x] Execute" (Windows NT 4). On Windows 2000 or XP, its a little different, you need to select "Execute Permissions: [Scripts and Executables]" from the dropdown. You do not need to reboot the computer after making the change, though on older systems it may be necessary to restart the web service.
Then make sure that the folder where your files are (not from IIS but from My Computer) that the IIS service has Execute permissions.
If this still doesn't work, you might want to take a gander at the PHP FAQs as they have very detailed explanations on how to setup PHP on IIS.
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