Go into SYS:Devs/DOSDrivers and find CD0 or CD1 and select with one mouse click and go to icon/information in the Workbench menu. Look for a a tooltypes entry of UNIT=0 and when you find the correct CD# entry then drag that icon out of the DOSDrivers drawer or delete it.
Your DOSDrivers mountlist entry is saying to mount a CD-ROM device at SCSI address 0 which doesn't exist and that is the reason for the error. The UNIT number is the SCSI address of the CD-ROM. Usually SCSI address 0 is a hard drive and CD-ROMs 3-5 on the Amiga.