Comment 22 for bug 1199529

I don't think it's as simple as a horizon problem... Looking at current stable/grizzly:

Installed /opt/stack/cinder
Processing dependencies for cinder==2013.1.5.a38.gc9c9eaa
error: Installed distribution python-keystoneclient 0.2.5 conflicts with requirement python-keystoneclient>=0.3.0

# grep keystoneclient /opt/stack/*/requirements.txt /opt/stack/*/tools/*requires*
/opt/stack/python-glanceclient/requirements.txt:python-keystoneclient>=0.3.0
/opt/stack/python-openstackclient/requirements.txt:python-keystoneclient>=0.4.1
/opt/stack/cinder/tools/pip-requires:python-keystoneclient>=0.2.0
/opt/stack/glance/tools/pip-requires:python-keystoneclient>=0.2.0
/opt/stack/keystone/tools/pip-requires:python-keystoneclient>=0.2.1,<0.3
/opt/stack/keystone/tools/test-requires:# for python-keystoneclient
/opt/stack/keystone/tools/test-requires:httplib2 # keystoneclient <0.2.1
/opt/stack/keystone/tools/test-requires:requests>=1.0.0 # replaces httplib2 in keystoneclient >=0.2.1