Lets see... First, lets make sure we have the right card. I'm guessing that your card is an Impact A2000-HC+2 ? The card has two 30pin simm sockets on the board?
If there is a ROM version problem, I would guess its the ROM on your SCSI card. That controller is an older GVP series I, and I'm not sure how well it supports CD-ROMS. Here are a few things to try.
#1 Change the SCSI ID of the CDROM. There should be jumpers on the back of the drive to do this.
#2 Change the termination on the CDROM. There is a jumper on the back of most SCSI CDROMS to enable/disable built in termination.
Now I'm not sure if the following will work (someone will tell me if I'm wrong), but you can give it a try.
#3 Goto
http://babel.org/amiga/#gvp and look on the page for the gvpscsi 3.15 BindDrivers driver. This should be the updated driver for your card, but for some reason it's named gvpscsi.device (not scsidev.device). Pop this in your SYS:expansion drawer. Maybe make a copy of it and rename it to scsidev.device and put that in your expansion drawer as well?? Make sure you have the bindriver command in your startup-sequence.
One last thing to keep in mind. Even if the system doesn't lock up when you scan the scsi bus, you wont be able to use a CDROM without additional software. I think I'm using amicdfs240.lha off of aminet.