Hi,
If you are getting this error up on starting a Xen VM, You can edit the grub type from xen configuration file.
vi /etc/xen/vm/vm101
#remove line:
kernel="/tmp/vmlinux.xxxxx"
#add this line:
bootloader="/usr/bin/pygrub"
Now rebuild the VM configuration file
xm create /etc/xen/vm/vm101.conf
The VM should start fine. Thanks