VPC web_flip can't find an interface to flip

[prb]

Trace as of 400629e was:

[DEBUG] (local) 02:34:52: AWS access configured. EC2 SSH as ubuntu using key /Users/me/.ssh/key.pem
[172.18.12.55] Executing task 'web_flip'
Traceback (most recent call last):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/fabric/main.py", line 732, in main
    *args, **kwargs
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/fabric/tasks.py", line 312, in execute
    multiprocessing
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/fabric/tasks.py", line 211, in _execute
    return task.run(*args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/fabric/tasks.py", line 121, in run
    return self.wrapped(*args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/fabric/decorators.py", line 135, in decorated
    decorated.return_value = func(*args, **kwargs)
  File "/Users/me/project/deployment/fabfile.py", line 81, in web_flip
    connect().assign_private_ip_addresses(current_node().interfaces[0].id,env.secondary_ip,allow_reassignment=True)
IndexError: list index out of range