unsupported pickle protocol: 3 with python 2.7

[xie186]

>>> from pickle import load
>>> with open('./test_data_dict.pckl', 'rb') as f:
...    data_dict = load(f)
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "/usr/lib64/python2.7/pickle.py", line 1378, in load
    return Unpickler(file).load()
  File "/usr/lib64/python2.7/pickle.py", line 858, in load
    dispatch[key](self)
  File "/usr/lib64/python2.7/pickle.py", line 886, in load_proto
    raise ValueError, "unsupported pickle protocol: %d" % proto
ValueError: unsupported pickle protocol: 3

What's the possible reason for this error? Thanks.

[unitemir]

:c