The EXS's conversion only handles Akai libraries through the S-3000 series. Once the S-5000 was released, Akai changed it's format, I believe to standard Wave files.
Chances are, you're trying to load an Akai S-5000 disk, which the EXS can't recognize.
You could probably put the CD in your drive, and the OS would see it as wave files, but you still wouldn't be able to access the actual Akai sampler instruments, that hold the key mapping, control info, etc...
You'll need to get a third party translator, like CDXtract to convert that to EXS, but that does work. I know, because I had a few of the S-5000 libraries, and CDXtract converted them effortlessly.