My laptop has restarted after showing the blue screen error. 

When I came back to my code on jupyter notebook and tried to submit a job, I got this error message:

UnpicklingError                           Traceback (most recent call last)
<ipython-input-17-171ae9eaaff0> in <module>
      1 h,j=OptProblem(H[2:4],Y[2:4])
----> 2 sampleset = dwave_sampler.sample_ising(h,j)
      3 #print(sampleset)

~\anaconda3\lib\site-packages\dimod\core\sampler.py in sample_ising(self, h, J, **parameters)
    262         """
    263         bqm = BinaryQuadraticModel.from_ising(h, J)
--> 264         return self.sample(bqm, **parameters)
    266     @samplemixinmethod

~\anaconda3\lib\site-packages\dwave\system\samplers\dwave_sampler.py in wrapper(sampler, *args, **kwargs)
     49         while True:
     50             try:
---> 51                 return f(sampler, *args, **kwargs)
     52             except SolverOfflineError as err:
     53                 if not sampler.failover:

~\anaconda3\lib\site-packages\dwave\system\samplers\clique.py in sample(self, bqm, chain_strength, **kwargs)
    388         # get the embedding
--> 389         embedding = find_clique_embedding(bqm.variables, self.target_graph,
    390                                           use_cache=True)

minorminer\busclique.pyx in minorminer.busclique.find_clique_embedding()

minorminer\busclique.pyx in minorminer.busclique.busgraph_cache.find_clique_embedding()

minorminer\busclique.pyx in minorminer.busclique.busgraph_cache._ensure_clique_cache()

minorminer\busclique.pyx in minorminer.busclique.busgraph_cache._fetch_cache()

minorminer\busclique.pyx in minorminer.busclique.busgraph_cache._fetch_cache()

minorminer\busclique.pyx in minorminer.busclique.busgraph_cache._fetch_cache()

minorminer\busclique.pyx in minorminer.busclique.busgraph_cache._fetch_cache()

UnpicklingError: invalid load key, '\x00'.

I'm not sure how to fix this issue!



  • Hello,

    You can resolve this issue by calling:


    or by removing the files manually.

    These files should be located in the directory indicated by:


    You can take a look at the docs here too:


    Would it be possible get a little more information about your system and setup?
    It would be very helpful in order for us to understand how this issue came about, so it can be avoided in the future.

    The following questions will help us better understand what might have happened to cause this state:

    1. What OS/Python/minorminer version do you have installed?
    2. Were you running code in multiple threads or in multiple processes?
    3. Did you happen to previously interrupt a calculation while it was embedding?

    In the near future, we will have some fixes for these issues as well.

    Thank you so much for your time and collaboration.

    Please let us know if you have any other questions.

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  • Hi David,

    Thanks for your response!

    1) I work on OS: Windows 10 Home, Python: 3.8.8, minorminer:0.2.6.

    2) I run my code normally without multiple threads or multiple processes.

    3) Sometimes, I lose internet connection, but I haven't encountered this issue before I got the blue screen error and the laptop restarted.

    If you need more details please let me know.


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  • Thank you so much for the information. It's definitely helpful.

    The bluescreen seems like the most likely culprit.

    This shouldn't be an issue in the not too distant future.

    Were you able to clear the cache and run the problem again?

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  • Yes, it works fine now.

    Thank you!

    Comment actions Permalink
  • That's great! 
    You are very welcome.
    Thanks again for reaching out.

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