Try to set quota of floating IP as 0 and allocate a floating IP for user.

2013-01-25 09:43:42 INFO nova.api.openstack.wsgi [req-35cbe242-3345-4fb5-9a41-a32fea528282 f2665c1140c54a03a98110cb86262ec3 dc32392af0ae4a098fb7235760077fa6] POST http://localhost:8774/v1.1/dc32392af0ae4a098fb7235760077fa6/os-floating-ips
2013-01-25 09:43:42 DEBUG nova.openstack.common.rpc.amqp [-] Making asynchronous call on network ... from (pid=25430) multicall path/nova/openstack/common/rpc/amqp.py:351
2013-01-25 09:43:42 DEBUG nova.openstack.common.rpc.amqp [-] MSG_ID is 6f7f1740b68d40a0a94dde47eca33c62 from (pid=25430) multicall path/nova/openstack/common/rpc/amqp.py:354
2013-01-25 09:43:42 ERROR nova.api.openstack [req-35cbe242-3345-4fb5-9a41-a32fea528282 f2665c1140c54a03a98110cb86262ec3 dc32392af0ae4a098fb7235760077fa6] Caught error: Maximum number of floating ips exceeded
Traceback (most recent call last):

  File "path/nova/openstack/common/rpc/amqp.py", line 275, in _process_data
    rval = self.proxy.dispatch(ctxt, version, method, **args)

  File "path/nova/openstack/common/rpc/dispatcher.py", line 145, in dispatch
    return getattr(proxyobj, method)(ctxt, **kwargs)

  File "path/nova/network/manager.py", line 279, in wrapped
    return func(self, context, *args, **kwargs)

  File "path/nova/network/manager.py", line 463, in allocate_floating_ip
    raise exception.FloatingIpLimitExceeded()

FloatingIpLimitExceeded: Maximum number of floating ips exceeded
2013-01-25 09:43:42 TRACE nova.api.openstack Traceback (most recent call last):
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/api/openstack/__init__.py", line 78, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     return req.get_response(self.application)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/webob/request.py", line 1053, in get_response
2013-01-25 09:43:42 TRACE nova.api.openstack     application, catch_exc_info=False)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/webob/request.py", line 1022, in call_application
2013-01-25 09:43:42 TRACE nova.api.openstack     app_iter = application(self.environ, start_response)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     return resp(environ, start_response)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/keystone/middleware/auth_token.py", line 176, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     return self.app(env, start_response)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     return resp(environ, start_response)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     return resp(environ, start_response)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     return resp(environ, start_response)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/routes/middleware.py", line 131, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     response = self.app(environ, start_response)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     return resp(environ, start_response)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 147, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     resp = self.call_func(req, *args, **self.kwargs)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 208, in call_func
2013-01-25 09:43:42 TRACE nova.api.openstack     return self.func(req, *args, **kwargs)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/api/openstack/wsgi.py", line 885, in __call__
2013-01-25 09:43:42 TRACE nova.api.openstack     content_type, body, accept)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/api/openstack/wsgi.py", line 933, in _process_stack
2013-01-25 09:43:42 TRACE nova.api.openstack     action_result = self.dispatch(meth, request, action_args)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/api/openstack/wsgi.py", line 1021, in dispatch
2013-01-25 09:43:42 TRACE nova.api.openstack     return method(req=request, **action_args)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/api/openstack/compute/contrib/floating_ips.py", line 188, in create
2013-01-25 09:43:42 TRACE nova.api.openstack     address = self.network_api.allocate_floating_ip(context, pool)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/network/api.py", line 199, in allocate_floating_ip
2013-01-25 09:43:42 TRACE nova.api.openstack     'auto_assigned': False}})
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/openstack/common/rpc/__init__.py", line 102, in call
2013-01-25 09:43:42 TRACE nova.api.openstack     return _get_impl().call(cfg.CONF, context, topic, msg, timeout)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/openstack/common/rpc/impl_kombu.py", line 712, in call
2013-01-25 09:43:42 TRACE nova.api.openstack     rpc_amqp.get_connection_pool(conf, Connection))
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/openstack/common/rpc/amqp.py", line 368, in call
2013-01-25 09:43:42 TRACE nova.api.openstack     rv = list(rv)
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/openstack/common/rpc/amqp.py", line 336, in __iter__
2013-01-25 09:43:42 TRACE nova.api.openstack     raise result
2013-01-25 09:43:42 TRACE nova.api.openstack FloatingIpLimitExceeded_Remote: Maximum number of floating ips exceeded
2013-01-25 09:43:42 TRACE nova.api.openstack Traceback (most recent call last):
2013-01-25 09:43:42 TRACE nova.api.openstack-
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/openstack/common/rpc/amqp.py", line 275, in _process_data
2013-01-25 09:43:42 TRACE nova.api.openstack     rval = self.proxy.dispatch(ctxt, version, method, **args)
2013-01-25 09:43:42 TRACE nova.api.openstack-
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/openstack/common/rpc/dispatcher.py", line 145, in dispatch
2013-01-25 09:43:42 TRACE nova.api.openstack     return getattr(proxyobj, method)(ctxt, **kwargs)
2013-01-25 09:43:42 TRACE nova.api.openstack-
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/network/manager.py", line 279, in wrapped
2013-01-25 09:43:42 TRACE nova.api.openstack     return func(self, context, *args, **kwargs)
2013-01-25 09:43:42 TRACE nova.api.openstack-
2013-01-25 09:43:42 TRACE nova.api.openstack   File "path/nova/network/manager.py", line 463, in allocate_floating_ip
2013-01-25 09:43:42 TRACE nova.api.openstack     raise exception.FloatingIpLimitExceeded()
2013-01-25 09:43:42 TRACE nova.api.openstack-
2013-01-25 09:43:42 TRACE nova.api.openstack FloatingIpLimitExceeded: Maximum number of floating ips exceeded
2013-01-25 09:43:42 TRACE nova.api.openstack-
2013-01-25 09:43:42 TRACE nova.api.openstack-
2013-01-25 09:43:42 INFO nova.api.openstack [req-35cbe242-3345-4fb5-9a41-a32fea528282 f2665c1140c54a03a98110cb86262ec3 dc32392af0ae4a098fb7235760077fa6] http://localhost:8774/v1.1/dc32392af0ae4a098fb7235760077fa6/os-floating-ips returned with HTTP 413
2013-01-25 09:43:42 INFO nova.osapi_compute.wsgi.server [req-35cbe242-3345-4fb5-9a41-a32fea528282 f2665c1140c54a03a98110cb86262ec3 dc32392af0ae4a098fb7235760077fa6] 127.0.0.1 - - [25/Jan/2013 09:43:42] "POST /v1.1/dc32392af0ae4a098fb7235760077fa6/os-floating-ips HTTP/1.1" 413 1095 0.512176