Do you need a CD drive in your virtual machine? I'd just leave it out of the configuration:
Code:
name = "grape"
uuid = "c3b505e0-b0fe-e8b5-03fb-093376019dbf"
maxmem = 256
memory = 256
vcpus = 1
builder = "hvm"
kernel = "/usr/lib/xen/boot/hvmloader"
boot = "c"
pae = 1
acpi = 1
apic = 1
localtime = 0
on_poweroff = "destroy"
on_reboot = "restart"
on_crash = "restart"
device_model = "/usr/lib64/xen/bin/qemu-dm"
sdl = 0
vnc = 0
vncunused = 0
vncdisplay = "-5900"
disk = [ "file:/xen/grape.img,hda,w" ]
vif = [ "mac=00:16:3e:56:66:6b,bridge=xenbr0" ]
serial = "pty"