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Ah never mind. @Genarito, the ThreadPoolExecutor is supposed to be used as a context manager. In your current code, the script ends and Python starts tearing itself down while `execute_error` is still running in a subprocess.
If you simply use the ThreadPoolExecutor to a context manager, the error goes away::
```python
from multiprocessing import Process
from concurrent.futures import ThreadPoolExecutor
def some_task():
 pass
def execute_error():
 p = Process(target=some_task)
 p.start()
 p.join()
 print(p.exitcode) # This is always 1 on a ThreadPoolExecutor!!!
# THIS IS THE IMPORTANT CHANGE
with ThreadPoolExecutor(max_workers=4) as executor:
 executor.submit(execute_error)
```