TypeError: expected string or buffer

  File "/home/prettygreen/pg/lib/payment/modules/protx/processor.py", line 196, in capture_payment
    transaction_id=self.transaction_id, reason_code=status) # using self.transaction_id for a test
  File "/home/prettygreen/pg/lib/payment/modules/base.py", line 143, in record_payment
    payment = recorder.capture_payment(amount=amount)
  File "/home/prettygreen/pg/lib/payment/modules/base.py", line 241, in capture_payment
    self.cleanup()
  File "/home/prettygreen/pg/lib/payment/modules/base.py", line 276, in cleanup
    order.order_success()
  File "/home/prettygreen/pg/lib/satchmo_store/shop/models.py", line 929, in order_success
    signals.order_success.send(self, order=self)
  File "/usr/lib/python2.4/site-packages/django/dispatch/dispatcher.py", line 150, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/home/prettygreen/pg/lib/satchmo_store/shop/notification.py", line 22, in order_success_listener
    send_order_confirmation(order)
  File "/home/prettygreen/pg/lib/satchmo_store/shop/notification.py", line 63, in send_order_confirmation
    email.send()
  File "/usr/lib/python2.4/site-packages/django/core/mail.py", line 275, in send
    return self.get_connection(fail_silently).send_messages([self])
  File "/usr/lib/python2.4/site-packages/django/core/mail.py", line 172, in send_messages
    sent = self._send(message)
  File "/usr/lib/python2.4/site-packages/django/core/mail.py", line 186, in _send
    email_message.message().as_string())
  File "/usr/lib/python2.4/site-packages/django/core/mail.py", line 246, in message
    msg.attach(self._create_attachment(*attachment))
  File "/usr/lib/python2.4/site-packages/django/core/mail.py", line 305, in _create_attachment
    mimetype, _ = mimetypes.guess_type(filename)
  File "/usr/lib64/python2.4/mimetypes.py", line 237, in guess_type
    return guess_type(url, strict)
  File "/usr/lib64/python2.4/mimetypes.py", line 103, in guess_type
    scheme, url = urllib.splittype(url)
  File "/usr/lib64/python2.4/urllib.py", line 935, in splittype
    match = _typeprog.match(url)