when I am trying to install OPENSTACK by using packstack..

I am getting this Error...

I dont know, how to resolve this problem.. please help me

ERROR : Error appeared during Puppet run: 192.168.40.50_keystone.pp Error: Could not prefetch keystone_role provider 'openstack': Execution of '/usr/bin/openstack role list --quiet --format csv' returned 1: Bad Gateway (HTTP 502)