I was having the same problem under 2.6.17-2-xen-k7 as reported by Markus Ingalsuo.
I have upgraded all xen packages to the unstable versions (using hypervisor 3.0.3 not 3.0-unstable), and I can now run two XenU at the same time: # xm list Name ID Mem(MiB) VCPUs State Time(s) Domain-0 0 140 1 r----- 21.6 vbind 4 64 1 -b---- 3.3 vhttp 3 256 1 -b---- 4.4 ii libc6-xen 2.3.6.ds1-7 GNU C Library: Shared libraries [Xen version] ii linux-image-2.6-xen-k7 2.6.18+3 Linux kernel 2.6 image on AMD K7 ii linux-image-2.6.18-1-xen-k7 2.6.18-3 Linux 2.6.18 image on AMD K7 ii linux-modules-2.6.18-1-xen-k7 2.6.18-3 Linux 2.6.18 modules on AMD K7 ii xen-hypervisor-3.0.3-1-i386 3.0.3-0-2 The Xen Hypervisor on i386 ii xen-linux-system-2.6.18-1-xen-k7 2.6.18-3 XEN system with Linux 2.6.18 image on AMD K7 ii xen-tools 2.7-4 Tools to manage debian XEN virtual servers ii xen-utils-3.0.3-1 3.0.3-0-2 XEN administrative tools ii xen-utils-common 3.0.3-0-1 XEN administrative tools - common files -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]