Active Directory cannot be joined

IT´s latest Rockstor Version and i get following error:
Traceback (most recent call last):
File “/opt/rockstor/src/rockstor/rest_framework_custom/generic_view.py”, line 41, in _handle_exception
yield
File “/opt/rockstor/src/rockstor/smart_manager/views/active_directory.py”, line 199, in post
smb_config = self._get_config(smbo)
File “/opt/rockstor/src/rockstor/smart_manager/views/base_service.py”, line 40, in _get_config
return json.loads(service.config)
File “/usr/lib64/python2.7/json/init.py”, line 338, in loads
return _default_decoder.decode(s)
File “/usr/lib64/python2.7/json/decoder.py”, line 366, in decode
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
TypeError: expected string or buffer