The full traceback is:
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/ansible/executor/task_executor.py", line 96, in run
    item_results = self._run_loop(items)
  File "/usr/lib/python2.7/dist-packages/ansible/executor/task_executor.py", line 296, in _run_loop
    res = self._execute(variables=task_vars)
  File "/usr/lib/python2.7/dist-packages/ansible/executor/task_executor.py", line 528, in _execute
    result = self._handler.run(task_vars=variables)
  File "/usr/lib/python2.7/dist-packages/ansible/plugins/action/include_vars.py", line 128, in run
    self._load_files(self.source_file)
  File "/usr/lib/python2.7/dist-packages/ansible/plugins/action/include_vars.py", line 233, in _load_files
    b_data, show_content = self._loader._get_file_contents(filename)
  File "/usr/lib/python2.7/dist-packages/ansible/parsing/dataloader.py", line 206, in _get_file_contents
    data = self._vault.decrypt(data, filename=b_file_name)
  File "/usr/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py", line 561, in decrypt
    plaintext, vault_id = self.decrypt_and_get_vault_id(vaulttext, filename=filename)
  File "/usr/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py", line 638, in decrypt_and_get_vault_id
    b_plaintext = this_cipher.decrypt(b_vaulttext, vault_secret)
  File "/usr/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py", line 1349, in decrypt
    b_plaintext = cls._decrypt_cryptography(b_ciphertext, b_crypted_hmac, b_key1, b_key2, b_iv)
  File "/usr/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py", line 1283, in _decrypt_cryptography
    decryptor.update(b_ciphertext) + decryptor.finalize()
  File "/usr/lib/python2.7/dist-packages/cryptography/hazmat/primitives/ciphers/base.py", line 149, in update
    return self._ctx.update(data)
  File "/usr/lib/python2.7/dist-packages/cryptography/hazmat/backends/openssl/ciphers.py", line 116, in update
    n = self.update_into(data, buf)
  File "/usr/lib/python2.7/dist-packages/cryptography/hazmat/backends/openssl/ciphers.py", line 127, in update_into
    "unsigned char *", self._backend._ffi.from_buffer(buf)
TypeError: from_buffer() cannot return the address of the raw string within a str or unicode or bytearray object

fatal: [hostimworkingon]: FAILED! => {
    "msg": "Unexpected failure during module execution.",
    "stdout": ""
}