Maas import-boot-images failed

Hi everybody,

I am installing MAAS on a virtual machine with KVM, i installed MAAS, created a superuser, but when i am trying to import boot images it failed. the /var/log/celery.log gives:

administrator@0-maascontroller0:~$ tail /var/log/maas/celery.log

[2015-04-14 11:11:26,591: INFO/Beat] Scheduler: Sending due task probe-dhcp-servers (provisioningserver.tasks.periodic_probe_dhcp)
[2015-04-14 11:11:26,594: INFO/MainProcess] Task provisioningserver.tasks.upload_dhcp_leases[341511d5-d82a-49cf-83c3-00faf058642a] succeeded in 0.0502586269995s: None
[2015-04-14 11:11:26,617: INFO/MainProcess] Received task: provisioningserver.tasks.periodic_probe_dhcp[11f00e4d-3dd6-4eeb-8cee-c53e1b8aa5a9] expires:[2015-04-14 09:12:26.592133+00:00]
[2015-04-14 11:11:29,724: INFO/MainProcess] Task provisioningserver.tasks.periodic_probe_dhcp[11f00e4d-3dd6-4eeb-8cee-c53e1b8aa5a9] succeeded in 3.106332222s: None
[2015-04-14 11:12:26,635: INFO/Beat] Scheduler: Sending due task unconditional-dhcp-lease-upload (provisioningserver.tasks.upload_dhcp_leases)
[2015-04-14 11:12:26,638: INFO/Beat] Scheduler: Sending due task probe-dhcp-servers (provisioningserver.tasks.periodic_probe_dhcp)
[2015-04-14 11:12:26,641: INFO/MainProcess] Received task: provisioningserver.tasks.upload_dhcp_leases[3e33886c-5ec2-4b43-8a2f-fc4d95df6ee2] expires:[2015-04-14 09:13:26.636631+00:00]
[2015-04-14 11:12:26,642: INFO/MainProcess] Received task: provisioningserver.tasks.periodic_probe_dhcp[3b0dc51d-4dfa-4193-bff0-e837f5d5f809] expires:[2015-04-14 09:13:26.639408+00:00]
[2015-04-14 11:12:26,741: INFO/MainProcess] Task provisioningserver.tasks.upload_dhcp_leases[3e33886c-5ec2-4b43-8a2f-fc4d95df6ee2] succeeded in 0.0979194359998s: None
[2015-04-14 11:12:29,883: INFO/MainProcess] Task provisioningserver.tasks.periodic_probe_dhcp[3b0dc51d-4dfa-4193-bff0-e837f5d5f809] succeeded in 3.136319937s: None

Any idea.