Failed to spawn an instance : AttributeError: 'str' object has no attribute 'fileno'

Tested trunk on Revision no 790.

If I start a new instance, it fails to spawn.
DescribeInstance status - Failed to spawn

nova-compute.log
-------------------------
2011-03-11 15:56:56,283 AUDIT nova.compute.manager [UEGXDCVTAY-IA6K1ILRO admin admin] instance 1: starting...
2011-03-11 15:56:56,399 DEBUG nova.rpc [-] Making asynchronous call... from (pid=17161) call /home/tpatil/recent/nova/nova/rpc.py:314
2011-03-11 15:56:56,399 DEBUG nova.rpc [-] MSG_ID is 5af3fe3eb20c47f5869fe3099c45c145 from (pid=17161) call /home/tpatil/recent/nova/nova/rpc.py:317
2011-03-11 15:56:56,683 DEBUG nova.rpc [-] Making asynchronous call... from (pid=17161) call /home/tpatil/recent/nova/nova/rpc.py:314
2011-03-11 15:56:56,684 DEBUG nova.rpc [-] MSG_ID is 5879905adc35407da03777f6bd77818a from (pid=17161) call /home/tpatil/recent/nova/nova/rpc.py:317
2011-03-11 15:56:57,103 DEBUG nova.virt.libvirt_conn [-] instance instance-00000001: starting toXML method from (pid=17161) to_xml /home/tpatil/recent/nova/nova/virt/libvirt_conn.py:679
2011-03-11 15:56:57,224 DEBUG nova.virt.libvirt_conn [-] instance instance-00000001: finished toXML method from (pid=17161) to_xml /home/tpatil/recent/nova/nova/virt/libvirt_conn.py:748
2011-03-11 15:56:57,264 INFO nova [-] called setup_basic_filtering in nwfilter
2011-03-11 15:56:57,264 INFO nova [-] ensuring static filters
2011-03-11 15:56:57,424 INFO nova [-] <nova.db.sqlalchemy.models.SecurityGroupIngressRule object at 0x96a1cec>
2011-03-11 15:56:57,424 INFO nova [-] <nova.db.sqlalchemy.models.SecurityGroupIngressRule object at 0x96a1a8c>
2011-03-11 15:56:57,438 DEBUG nova.utils [-] Running cmd (subprocess): sudo iptables-save -t filter from (pid=17161) execute /home/tpatil/recent/nova/nova/utils.py:148
2011-03-11 15:56:57,446 DEBUG nova.utils [-] Running cmd (subprocess): sudo iptables-restore from (pid=17161) execute /home/tpatil/recent/nova/nova/utils.py:148
2011-03-11 15:56:57,454 DEBUG nova.utils [-] Running cmd (subprocess): sudo iptables-save -t nat from (pid=17161) execute /home/tpatil/recent/nova/nova/utils.py:148
2011-03-11 15:56:57,460 DEBUG nova.utils [-] Running cmd (subprocess): sudo iptables-restore from (pid=17161) execute /home/tpatil/recent/nova/nova/utils.py:148
2011-03-11 15:56:57,466 DEBUG nova.utils [-] Running cmd (subprocess): sudo ip6tables-save -t filter from (pid=17161) execute /home/tpatil/recent/nova/nova/utils.py:148
2011-03-11 15:56:57,473 DEBUG nova.utils [-] Running cmd (subprocess): sudo ip6tables-restore from (pid=17161) execute /home/tpatil/recent/nova/nova/utils.py:148
2011-03-11 15:56:57,479 DEBUG nova.utils [-] Result was 2 from (pid=17161) execute /home/tpatil/recent/nova/nova/utils.py:161
2011-03-11 15:56:57,479 DEBUG nova.utils [-] ['sudo', 'ip6tables-restore'] failed. Retrying. from (pid=17161) execute /home/tpatil/recent/nova/nova/utils.py:178
2011-03-11 15:56:58,085 DEBUG nova.utils [-] Running cmd (subprocess): sudo ip6tables-restore from (pid=17161) execute /home/tpatil/recent/nova/nova/utils.py:148
2011-03-11 15:56:58,085 ERROR nova.exception [-] Uncaught exception
(nova.exception): TRACE: Traceback (most recent call last):
(nova.exception): TRACE: File "/home/tpatil/recent/nova/nova/exception.py", line 120, in _wrap
(nova.exception): TRACE: return f(*args, **kw)
(nova.exception): TRACE: File "/home/tpatil/recent/nova/nova/virt/libvirt_conn.py", line 407, in spawn
(nova.exception): TRACE: self.firewall_driver.prepare_instance_filter(instance)
(nova.exception): TRACE: File "/home/tpatil/recent/nova/nova/virt/libvirt_conn.py", line 1252, in prepare_instance_filter
(nova.exception): TRACE: self.iptables.apply()
(nova.exception): TRACE: File "/home/tpatil/recent/nova/nova/utils.py", line 524, in inner
(nova.exception): TRACE: return f(*args, **kwargs)
(nova.exception): TRACE: File "/home/tpatil/recent/nova/nova/network/linux_net.py", line 302, in apply
(nova.exception): TRACE: attempts=5)
(nova.exception): TRACE: File "/home/tpatil/recent/nova/nova/utils.py", line 153, in execute
(nova.exception): TRACE: stdout=stdout, stderr=stderr, env=env)
(nova.exception): TRACE: File "/usr/lib/pymodules/python2.6/eventlet/green/subprocess.py", line 25, in __init__
(nova.exception): TRACE: subprocess_orig.Popen.__init__(self, args, 0, *argss, **kwds)
(nova.exception): TRACE: File "/usr/lib/python2.6/subprocess.py", line 626, in __init__
(nova.exception): TRACE: errread, errwrite) = self._get_handles(stdin, stdout, stderr)
(nova.exception): TRACE: File "/usr/lib/python2.6/subprocess.py", line 983, in _get_handles
(nova.exception): TRACE: c2pwrite = stdout.fileno()
(nova.exception): TRACE: AttributeError: 'str' object has no attribute 'fileno'
(nova.exception): TRACE:
2011-03-11 15:56:58,087 ERROR nova.compute.manager [UEGXDCVTAY-IA6K1ILRO admin admin] instance 1: Failed to spawn
(nova.compute.manager): TRACE: Traceback (most recent call last):
(nova.compute.manager): TRACE: File "/home/tpatil/recent/nova/nova/compute/manager.py", line 213, in run_instance
(nova.compute.manager): TRACE: self.driver.spawn(instance_ref)
(nova.compute.manager): TRACE: File "/home/tpatil/recent/nova/nova/exception.py", line 126, in _wrap
(nova.compute.manager): TRACE: raise Error(str(e))
(nova.compute.manager): TRACE: Error: 'str' object has no attribute 'fileno'