I've got ImageFX 4.5 installed under Amiga Forever 08. I am using a custom virtual 68040 A4000 Amiga setup partition with OS3.9.
I vaguely seem to recall that I had initial problems getting UAE to work the the ImageFX install disk. I know the ImageFX install CD has some sort of copy protection on it (I made a backup of my original disk once, just by dumping all the files onto my hard drive from the CD, then burning them to a new CD - it didn't work. I had to make a byte for byte copy of the original disk - clone disk - to have a functioning backup install CD).
This might be part of the problem. If UAE is just mounting anything in the PC's CD-ROM drive as a generic removable media (which UAE can do), then the Amiga won't be able to access whatever copy protection bits there are on the install CD. It won't 'know' it is a CD-ROM that's being accessed. I vaguely recall that I had to ensure that UAE was using the Amiga's own CD0: device to mount the CD-ROM drive.