[Build-14]:UI:"Internal Server Error" while associating an instance to a floating IP"

An association of instance with a Floating IP is giving error saying to add valid instance.
The instance has been selected from the drop down available.
The above operation is a success through open-stack

The network was created successfully .

The snapshot is attached.
setup info
:
host1 = 'root@10.204.216.63'
host2 = 'root@10.204.216.64'
host3 = 'root@10.204.216.65'
host4 = 'root@10.204.216.66'
host5 = 'root@10.204.216.67'
env.roledefs = {
    'all': [host1, host2, host3, host4, host5],
    'cfgm': [host1, host2, host3],
    'openstack': [host2],
    'control': [host2, host3],
    'compute': [host4, host5],
    'collector': [host1],
    'webui': [host1],
    'database': [host1, host2],
    'build': [host_build],
}

env.hostnames = {
    'all': ['nodec6', 'nodec7', 'nodec8', 'nodec9', 'nodec10']
}