Deployment failed in experimental mode after upgrade fuel

Steps.

1. Deploy master 6.1
2. Upgrade master to 7.0
3. enable experimental mode
4. create 6.1 ubuntu cluster on 7.0 fuel
5. Run network verification
6. Deploy cluster

Actual result:
Deployment failed with following error:
Error
Failed to execute hook 'shell' Failed to run command cd / && fa_build_image --image_build_dir /var/lib/fuel/ibp --log-file /var/log/fuel-agent-env-1.log --data_driver nailgun_build_image --input_data '{"image_data": {"/boot": {"container": "gzip", "uri": "http://10.109.0.2:8080/targetimages/env_1_ubuntu_1404_amd64-boot.img.gz", "format": "ext2"}, "/": {"container": "gzip", "uri": "http://10.109.0.2:8080/targetimages/env_1_ubuntu_1404_amd64.img.gz", "format": "ext4"}}, "output": "/var/www/nailgun/targetimages", "repos": [{"name": "ubuntu", "section": "main universe multiverse", "uri": "http://archive.ubuntu.com/ubuntu/", "priority": null, "suite": "trusty", "type": "deb"}, {"name": "ubuntu-updates", "section": "main universe multiverse", "uri": "http://archive.ubuntu.com/ubuntu/", "priority": null, "suite": "trusty-updates", "type": "deb"}, {"name": "ubuntu-security", "section": "main universe multiverse", "uri": "http://archive.ubuntu.com/ubuntu/", "priority": null, "suite": "trusty-security", "type": "deb"}, {"name": "mos", "section": "main restricted", "uri": "http://10.109.0.2:8080/2014.2.2-6.1/ubuntu/x86_64", "priority": 1050, "suite": "mos6.1", "type": "deb"}, {"name": "mos-updates", "section": "main restricted", "uri": "http://mirror.fuel-infra.org/mos/ubuntu/", "priority": 1050, "suite": "mos6.1-updates", "type": "deb"}, {"name": "mos-security", "section": "main restricted", "uri": "http://mirror.fuel-infra.org/mos/ubuntu/", "priority": 1050, "suite": "mos6.1-security", "type": "deb"}, {"name": "mos-holdback", "section": "main restricted", "uri": "http://mirror.fuel-infra.org/mos/ubuntu/", "priority": 1100, "suite": "mos6.1-holdback", "type": "deb"}, {"name": "Auxiliary", "section": "main restricted", "uri": "http://10.109.0.2:8080/2014.2.2-6.1/ubuntu/auxiliary", "priority": 1150, "suite": "auxiliary", "type": "deb"}], "codename": "trusty"}'

Version:
[root@nailgun ~]# cat /etc/fuel/version.yaml
VERSION:
  feature_groups:
    - mirantis
    - experimental
  production: "docker"
  release: "7.0"
  openstack_version: "2015.1.0-7.0"
  api: "1.0"
  build_number: "301"
  build_id: "301"
  nailgun_sha: "4162b0c15adb425b37608c787944d1983f543aa8"
  python-fuelclient_sha: "486bde57cda1badb68f915f66c61b544108606f3"
  fuel-agent_sha: "50e90af6e3d560e9085ff71d2950cfbcca91af67"
  fuel-nailgun-agent_sha: "d7027952870a35db8dc52f185bb1158cdd3d1ebd"
  astute_sha: "6c5b73f93e24cc781c809db9159927655ced5012"
  fuel-library_sha: "5d50055aeca1dd0dc53b43825dc4c8f7780be9dd"
  fuel-ostf_sha: "2cd967dccd66cfc3a0abd6af9f31e5b4d150a11c"
  fuelmain_sha: "a65d453215edb0284a2e4761be7a156bb5627677"
[root@nailgun ~]#