Install Trixbox-2.8.0.4.iso on CenServer by Iso Store - Error from bootloader: too many boottable disks (2 disks).

Hi!
I installed trixbox-2.8.0.4 from iso store. It required HVM, then I enable HVM follow as:
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1.) Go to any XenConsole.
Get the UUID of the VM with “xe vm-list”.

[root@xen01 ~]# xe vm-list
uuid ( RO) : 734482f0-d486-5e34-8867-2e87449605af
name-label ( RW): trixbox-2.8.0.4
power-state ( RO): halted

2.) Now make the HDD of the VM bootable.
Get the VBD-UUID. Get it with:
“xe vm-disk-list uuid=734482f0-d486-5e34-8867-2e87449605af” .

[root@xen01 ~]# xe vm-disk-list uuid=734482f0-d486-5e34-8867-2e87449605af
Disk 0 VBD:
uuid ( RO) : b2d4dcff-7f17-5d3c-b594-530a805823cf
vm-name-label ( RO): trixbox-2.8.0.4
userdevice ( RW): 1

Disk 0 VDI:
uuid ( RO) : 192893b8-edca-4917-83ee-4cc7b4715a5b
name-label ( RW): trixbox-2.8.0.1
sr-name-label ( RO): Local storage
virtual-size ( RO): 10737418240

3.) Make the VM paravirtualized – at the host console run:

xe vm-param-clear uuid=734482f0-d486-5e34-8867-2e87449605af param-name=HVM-boot-policy
xe vm-param-set uuid=734482f0-d486-5e34-8867-2e87449605af PV-bootloader=pygrub
xe vm-param-set uuid=734482f0-d486-5e34-8867-2e87449605af PV-args=”utf8″

Activate the Blockdevice of the HDD and make it bootable: (Dit is dus Disk 0 VBD:)
xe vbd-param-set uuid=b2d4dcff-7f17-5d3c-b594-530a805823cf bootable=true

Unmount CDROM!! Otherwise you wil get the too many bootable disks warning!
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I don’t know what do I umount?

But, when I reboot to install, it was error.
The bootloader for this VM returned an error — did the VM installation succed? Error from bootloader: too many boottable disks (2 disks).
thank you very much!