[libvirt] cannot migrate vm back to original machine

I am running Fedora 8 with Xen 3.1.2 and libvirt 0.4.3 on two machines (machine #1 and #2). I am using virDomainMigrate() to migrate a VM from machine #2 (where it originally resides) to machine #1. I am unable to migrate the VM back to machine #2 using virDomainMigrate(), even if I first migrate the VM from #2 to #1 by hand, using "xm migrate -l <vmname> <ipaddress1>". When I make the call to virDomainMigrate(domain_to_migrate, connection_to_machine_2, VIR_MIGRATE_LIVE, NULL, NULL, 0), I get the following message: libvir: Xen Daemon error : POST operation failed: xend_post: error from xen daemon: (xend.err "can't connect: Name or service not known") I have tried running my program on both machine #2 (connecting to machine #1 with ssh, and machine #2 with local (NULL) or ssh), and on a separate 3rd machine (connecting to machine #1 and #2 with ssh), but I get the same error message in both cases. I've tried connecting with both virConnectOpen() and virConnectOpenReadOnly(). I don't see any obvious error messages when running libvirtd -- verbose, other than the one above, which shows up on machine #1. There are no obvious error messages in libvirtd --verbose on machine #2. I checked /var/log/xen/xend.log and xend-debug.log, but didn't see any error message there either. My /etc/xen/xend-config.sxp is set with default loglevel of DEBUG. Any clues as to why I cannot migrate the VM back to the original machine with libvirt? I am able to migrate it back from #1 to #2 by hand using "xm migrate -l <vmname> <ipaddress2>". Thanks, Elaine