After I reboot but I get this when calling xm : 
xm dmesg                                                
WARING!  Can't find version 3.4 of xen utils, fallback to default version!
Error: Unable to connect to xend: No such file or directory. Is xend running?
When I execute xend I get : 
xend 
WARING!  Can't find version 3.4 of xen utils, fallback to default version!
ERROR Internal error: Could not obtain handle on privileged command interface (2 = No such file or directory)
Traceback (most recent call last):
  File "/usr/lib/xen-default/bin/xend", line 38, in <module>
    from xen.xend.server import SrvDaemon
  File "/usr/lib/xen-4.0/lib/python/xen/xend/server/SrvDaemon.py", line 26, in <module>
    import relocate
  File "/usr/lib/xen-4.0/lib/python/xen/xend/server/relocate.py", line 28, in <module>
    from xen.xend import XendDomain
  File "/usr/lib/xen-4.0/lib/python/xen/xend/XendDomain.py", line 36, in <module>
    from xen.xend import XendOptions, XendCheckpoint, XendDomainInfo
  File "/usr/lib/xen-4.0/lib/python/xen/xend/XendCheckpoint.py", line 20, in <module>
    from xen.xend import balloon, sxp, image
  File "/usr/lib/xen-4.0/lib/python/xen/xend/image.py", line 46, in <module>
    xc = xen.lowlevel.xc.xc()
xen.lowlevel.xc.Error: (1, 'Internal error', 'Could not obtain handle on privileged command interface (2 = No such file or directory)')
Does this has to do with the kernel I'm booting ?
My /boot looks like this : 
System.map-2.6.32-5-xen-amd64  
initrd.img-2.6.32-5-xen-amd64
config-2.6.32-5-xen-amd64      
vmlinuz-2.6.32-5-xen-amd64
grub                           
xen-4.0-amd64.gz
And my menu.lst looks like this : 
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#
### BEGIN /etc/grub.d/40_custom ###
default 0
timeout 1
title 2.6.32-5-xen-amd64
  root (hd0)
  kernel /boot/vmlinuz-2.6.32-5-xen-amd64 root=/dev/xvda1 ro
  initrd /boot/initrd.img-2.6.32-5-xen-amd64
### END /etc/grub.d/40_custom ###
I have been trying to get around this but ... nothing works ! 
Any help would be much appreciated, thanks in advance !
-Xavier