How to resolve ajenti import core problem?

 ajenti-panel -v result is:

31.03.2018 09:08 ajenti-panel:105              INFO  Using config file /etc/ajenti/config.json
31.03.2018 09:08 ajenti-panel:130              INFO  Ajenti starting in foreground
Traceback (most recent call last):
  File "/usr/bin/ajenti-panel", line 137, in <module>
    from ajenti import core
  File "/usr/lib/python2.7/site-packages/ajenti/core.py", line 21, in <module>
    from ajenti.middleware import SessionMiddleware, AuthenticationMiddleware
  File "/usr/lib/python2.7/site-packages/ajenti/middleware.py", line 11, in <module>
    from ajenti.users import UserManager
  File "/usr/lib/python2.7/site-packages/ajenti/users.py", line 3, in <module>
    from passlib.hash import sha512_crypt
  File "/usr/lib/python2.7/site-packages/passlib/hash.py", line 22, in <module>
    from passlib.registry import _proxy
  File "/usr/lib/python2.7/site-packages/passlib/registry.py", line 11, in <module>
    from passlib.utils import is_crypt_handler
  File "/usr/lib/python2.7/site-packages/passlib/utils/__init__.py", line 32, in <module>
    from passlib.utils.compat import add_doc, b, bytes, join_bytes, join_byte_values, \
ImportError: cannot import name b

[root@server ~]# service ajenti start
Starting Ajenti:
31.03.2018 09:10 INFO  Using config file /etc/ajenti/config.json
started                                                    [  OK  ]

[root@server ~]# service ajenti status
Ajenti is not running                                      [  OK  ]

How can I resolve this problem?