Xen users - Jan 2013 - Xen 4.1 kernel error on the IBM x3650 M4

Hi,

Installed Ubuntu 12.04 LTS Server on the hardware.

Base install goes OK as does installing Xen kernel 
(xen-hypervisor-amd64) but on reboot get the error
(Not enough memory to relocate the dom0 kernel image).

Tried changing dom0_mem with no success.

Any ideas what to try next?

Thanks
Richard