It happened when I attended virt test day(http://fedoraproject.org/wiki/Test_Day:2011-04-14_Virtualization) to run the test:

http://fedoraproject.org/wiki/QA:Testcase_Live_Migration_using_libvirt/virsh

I can confirm this running F15 with the latest updates. NFS is used as shared storage.

This is some extra info from within virt-manager

Unable to migrate guest: internal error unable to execute QEMU command 'migrate': An undefined error has ocurred
Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 45, in cb_wrapper
    callback(asyncjob, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/migrate.py", line 523, in _async_migrate
    vm.migrate(dstconn, migrate_uri, rate, live, secure, meter=meter)
  File "/usr/share/virt-manager/virtManager/domain.py", line 1222, in migrate
    self._backend.migrate(destconn.vmm, flags, newname, interface, rate)
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 521, in migrate
    if ret is None:raise libvirtError('virDomainMigrate() failed', dom=self)
libvirtError: internal error unable to execute QEMU command 'migrate': An undefined error has ocurred

Vincent

This package has changed ownership in the Fedora Package Database.  Reassigning to the new owner of this component.

This package has changed ownership in the Fedora Package Database.  Reassigning to the new owner of this component.

This package has changed ownership in the Fedora Package Database.  Reassigning to the new owner of this component.

This package has changed ownership in the Fedora Package Database.  Reassigning to the new owner of this component.

This package has changed ownership in the Fedora Package Database.  Reassigning to the new owner of this component.

This package has changed ownership in the Fedora Package Database.  Reassigning to the new owner of this component.

Sorry for the general lack of response, but since F15 is very close to EOL, closing this as WONTFIX. If anyone can still reliably reproduce this issue on F16 or higher, please reopen.

I can reproduce it on RHEL 6.3. 

Reopening changing the product

Since this BZ is a clone to F15 of a BZ created 2 years ago for RHEL6.0, you weren't the reporter of the original BZ or of the clone, and the migration code (along with the rest of libvirt) has changed immensely in the last 3 years, I think it's highly unlikely to have the same root cause, and better results would be achieved by filing a new BZ with details of  exactly what your setup is, what action you took, and exactly what were the results.

I'm re-closing this bug in anticipation of you opening a new one.

(I would recommend against re-cloning this BZ; the information it contains is severely out of date, and will only serve to confuse.)