Fedora xen - May 2007 - domU crash whith auto-boot

Hello,
I have a Dell 2950 with :

kernel-xen.i686                          2.6.18-1.2798.fc6      
installed      xen.i386                                 
3.0.3-8.fc6            installed      
xen-libs.i386                            3.0.3-8.fc6            installed

When I restart domU with dom0 reboot or /etc/init.d/xendomains script I 
have this error
in my xend.log :

[2007-05-14 14:20:07 xend.XendDomainInfo 7870] WARNING 
(XendDomainInfo:882) Domain has crashed: name=xxxx id=21.
[2007-05-14 14:20:08 xend.XendDomainInfo 7870] ERROR 
(XendDomainInfo:1675) VM xxxx restarting too fast (7.688173 seconds 
since the last restart).  Refusing to restart to avoid loops.

on eight domU I have only six which restart normally and two with this 
error.

An idea ?