/var/log/nova/nova-consoleauth.log: ERROR nova.rpc.amqp [req-6eb532ae-b024-4ada-8bb5-95ebc132dd2f None None] Exception during message handling
TRACE nova.rpc.amqp Traceback (most recent call last):
TRACE nova.rpc.amqp   File "/usr/lib/python2.7/dist-packages/nova/rpc/amqp.py", line 253, in _process_data
TRACE nova.rpc.amqp     rval = node_func(context=ctxt, **node_args)
TRACE nova.rpc.amqp   File "/usr/lib/python2.7/dist-packages/nova/consoleauth/manager.py", line 102, in check_token
TRACE nova.rpc.amqp     if token_valid and self._validate_console(token):
TRACE nova.rpc.amqp   File "/usr/lib/python2.7/dist-packages/nova/consoleauth/manager.py", line 91, in _validate_console
TRACE nova.rpc.amqp     console_valid = self.compute_api.validate_vnc_console(context,
TRACE nova.rpc.amqp NameError: global name 'context' is not defined

1, unzip file
    tar xvzf openstack_novnc.tar.gz
2, apply the patch diffs by running this commands on your root shell:
    patch -p0 < api.py.diff
    patch -p0 < manager.py.diff
    patch -p0 < test_compute.py.diff
 
URL:　http://ispire.me/fix-for-broken-vnc-console-on-openstack-essex-under-debianubuntu/