[CentOS-virt] xen

Have anyone get a ubuntu guest worked in centos?
I try now but only recive errors
insmod: error inserting '/lib/scsi_mod.ko': -1 Operation not permitted

Loading sd_mod.ko module

ksign: module signed with unknown public key

- signature keyid: 88a2b9299d40c296 ver=3

insmod: error inserting '/lib/sd_mod.ko': -1 Operation not permitted

Loading libata.ko module

ksign: module signed with unknown public key

- signature keyid: 88a2b9299d40c296 ver=3

insmod: error inserting '/lib/libata.ko': -1 Operation not permitted

Loading ata_piix.ko module

ksign: module signed with unknown public key

- signature keyid: 88a2b9299d40c296 ver=3

insmod: error inserting '/lib/ata_piix.ko': -1 Operation not permitted

Loading dm-mod.ko module

ksign: module signed with unknown public key

- signature keyid: 88a2b9299d40c296 ver=3

insmod: error inserting '/lib/dm-mod.ko': -1 Operation not permitted

Loading dm-log.ko module

ksign: module signed with unknown public key

- signature keyid: 88a2b9299d40c296 ver=3

insmod: error inserting '/lib/dm-log.ko': -1 Operation not permitted

Loading dm-mirror.ko module

I use
kernel = "/boot/vmlinuz-2.6.18-128.el5xen"                      
ramdisk = "/boot/initrd-2.6.18-128.1.6.el5xen"
Any tip?