I'm quite sure that I kow what your problem is because, I had same problem, first check dh0:devs\dosdriver\cd0 with text editor there are probaly atapi.device and cachecfs.
Now it bit hard for me to remember how did I actually solved problem, but reason is when you installed cd-rom support you HAD a CD-rom support allready installed, intaller didn't overwrite old ones.
First what I remember sure, IF you have atapi.device in dh0:/devs/dosdrivers/cd0 just write it over with (you remember you have opened it with text editor?) scsi.device, don't worry you woun't find it it's inside of A OS 3.9 rom update
Now I don't remember do you need to delete cachecdfs allso, it might have came with IDEFIX paggage???
BUT copy whole "install cd support" directory from amiga os install cd to your hd before you start to delete anything
