Command emails failing during signature

[pb30]

Emailing the command address errors out with:

character mapping must return integer, None or unicode: TypeError
Traceback (most recent call last):
File "/var/task/lambda.py", line 18, in lambda_handler
handle_command(command_address, msg)
File "/var/task/control/__init__.py", line 71, in handle_command
subject='Re:
{}
'.format(sign(subject, reply_to)),
File "/var/task/control/__init__.py", line 137, in sign
signature(' '.join([ reply_to, timestamp, subject, ])),
File "/var/task/control/__init__.py", line 131, in signature
return base64.b64encode(hmac.new(signing_key, cmd.strip(), hashlib.sha1).digest())
File "/usr/lib64/python2.7/hmac.py", line 136, in new
return HMAC(key, msg, digestmod)
File "/usr/lib64/python2.7/hmac.py", line 75, in __init__
self.outer.update(key.translate(trans_5C))
TypeError: character mapping must return integer, None or unicode

config.py has: signing_key = u'dUQtPCwq8C3jwpQdRG7cJe2Gu5KgCA'