What does "ERROR - Can't compile non template nodes" in Airflow with the PapermillOperator mean?

Question

I'm running my first Papermill task, which is to run a Jupyter notebook. Here is the operator:

t5 = PapermillOperator(
    task_id="run_example_notebook",
    input_nb=path2,
    output_nb=path2,
    parameters={"msgs": "Ran from Airflow at {{ execution_date }}!"},
    dag=dag,
)

I think the file path is correct:

path2 = os.path.join(os.path.dirname(__file__),'../amazon_visualization3.ipynb')

Then, the following error occurs:

ERROR - Can't compile non template nodes

Anyone know what I'm doing wrong?