SystemError: error return without exception set

[Natalie Leung]

I am trying to use Python to communicate and send commands in MSC Marc. A part of the code looks something like this:

from py_mentat import*

directory = '[specified the file path to my model]' 
marcModel = '[name of my model]' 

py_echo(0)
openModel = '*new_model yes *open_model "'+ directory + marcModel +'"'
py_send(openModel)


The code stops at "py_send(openModel)" with an error message that reads: Traceback (most recent call last): File "[my file path]", line 11, in py_send(openModel)
SystemError: error return without exception set

I tried running the code on different platforms (e.g. Command Prompt, Wing 101, python.exe) and I get the same result. What could be the problem?