If you have an Ultra 5/10 with two IDE drives and a CD-ROM, then you need to update the cdrom device alias in the EEPROM as below;
Original;
devalias
cdrom /pci@1f,0/pci@1,1/ide@3/cdrom@2,0:f
If the CD-ROM is a slave on the primary controller:
ok nvalias cdrom /pci@1f,0/pci@1,1/ide@3/cdrom@1,0:f
If the CD-ROM is a slave on the secondary controller:
ok nvalias cdrom /pci@1f,0/pci@1,1/ide@3/cdrom@3,0:f
You should now be able to boot from your cdrom.