In case anyone else comes along, I had the same problem using Apache 2.4.6 (Ubuntu). It had to do with apache not having permission to /usr/lib/iipimage-server. I simply copied that to /usr/share/iipimage-server and adjusted the path in iipsrv.conf and the url worked.
The easiest way to sound like a professional when you talk about photography these days is to grumble about the deficiencies of RAW file converters. The ability to save pictures in RAW format rather than JPEG or TIFF is what distinguishes a "pro level" camera from a consumer device. But rather than mentioning your camera's specs outright, the shrewd move is the heavy sigh followed by lamentations about your tireless search for the perfect software to properly manipulate your beautiful work. Let's take a look at how to do it using Linux and open source.