I am trying to use devstack to install OpenStack in my RHEL 6.5 (Python 2.6.6) machine, but it failed:

2015-01-16 10:08:33.271 | + openstack --os-token admin --os-url=http://192.168.122.153:5000/v3 --os-identity-api-version=3 role add --user heat_domain_admin --domain bc62352ee799440fb527b2c8fd64ee46 admin

2015-01-16 10:08:33.496 | /usr/lib/python2.6/site-packages/keystoneclient/access.py:20: DeprecationWarning: The oslo namespace package is deprecated. Please use oslo_utils instead.

2015-01-16 10:08:33.498 |   from oslo.utils import timeutils

2015-01-16 10:08:33.509 | /usr/lib/python2.6/site-packages/keystoneclient/i18n.py:21: DeprecationWarning: The oslo namespace package is deprecated. Please use oslo_i18n instead.

2015-01-16 10:08:33.510 |   from oslo import i18n

2015-01-16 10:08:33.524 | /usr/lib/python2.6/site-packages/keystoneclient/session.py:20: DeprecationWarning: The oslo namespace package is deprecated.Please use oslo_config instead.

2015-01-16 10:08:33.526 |   from oslo.config import cfg

2015-01-16 10:08:33.541 | /usr/lib/python2.6/site-packages/keystoneclient/session.py:21: DeprecationWarning: The oslo namespace package is deprecated.Please use oslo_serialization instead.

2015-01-16 10:08:33.542 |   from oslo.serialization import jsonutils

**2015-01-16 10:08:34.734 | ERROR: openstack An unexpected error prevented the server from fulfilling your request: 'module' object has no attribute 'getcallargs' (Disable debug mode to suppress these details.) (HTTP 500)**

Any ideas about what happened? Thanks!