title: Unable to pickle load ==> KeyError: '_unlocked'
body: <p>Python version: 3.8.10
  Pickle version: 4.0</p>
  <p>Old Python version: 3.8.5</p>
  <p>Recently, I updated my python environment, but since then have probles loading data using pickle.
  The code is as follows:</p>
  <pre><code>     with  open(retr_folder+&quot;\\PIPELINE&quot;, &quot;rb&quot; ) as f:
              print(f)
              p = pickle.load(f)
  </code></pre>
  <p>However, using this function results into an Keyerror:</p>
  <pre><code>    p = pickle.load(f)
  
    File ~\anaconda3\lib\site-packages\mne\io\meas_info.py:867 in __setstate__
      self._unlocked = state['_unlocked']
  
  KeyError: '_unlocked'
  </code></pre>
  <p>Pipeline is an <strong>object</strong> saved on te disk that was instantiated by:</p>
  <pre><code>class PipeLine():
      def __init__(self, inputs=()):
          self.info = []
          self.subjects_dir=[]
          self.waves =[]
          self.file_names=[]
  </code></pre>
  <p>I am hoping someone can help me with this problem.</p>