DemoPythonGrader not working in Coursera: "exec user process caused: no such file or directory"

[ShawnHymel]

I'm trying to get DemoPythonGrader to work in Coursera. It uploads fine, but when I submit an assignment, I get the following error:

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-- Resource limits : -------
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{'CPU': 1, 'Memory': 4096}
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-- Environment Variables: --
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filename=multiply.py
userId=44528918
partId=M3Ra5
PART_TITLE=Multiply
----------------------------
standard_init_linux.go:219: exec user process caused: no such file or directory

I created 2 parts of a new assignment in a test course on Coursera. I changed the partId's in the testCases.py file to the partId's generated by Coursera. I zipped up the contents of the autograder/ directory (not the directory itself) and uploaded the .zip file as my autograder. I switched to learner view and tried to upload the flipSign.py and multiply.py files. The grader failed with the above error. Any help would be appreciated.