Cannot open Jupyter Notebook

When I try to create a new Anaconda environment, I cannot load Jupyter Notebook. I get following error:

Traceback (most recent call last):
File “C:\Users\X\Anaconda3\envs\Stellargraph\Scripts\”, line 6, in
from notebook.notebookapp import main
File “C:\Users\X\Anaconda3\envs\Stellargraph\lib\site-packages\notebook\”, line 49, in
from zmq.eventloop import ioloop
File “C:\Users\X\Anaconda3\envs\Stellargraph\lib\site-packages\zmq\eventloop_ init”, line 3, in
from zmq.eventloop.ioloop import IOLoop
File “C:\Users\X\Anaconda3\envs\Stellargraph\lib\site-packages\zmq\eventloop\”, line 78, in
while _IOLoop.configurable_default() is not _IOLoop:
File “C:\Users\X\Anaconda3\envs\Stellargraph\lib\site-packages\tornado\”, line 328, in configurable_default
from tornado.platform.asyncio import AsyncIOLoop
File “C:\Users\X\Anaconda3\envs\Stellargraph\lib\site-packages\tornado\platform\”, line 34, in
AttributeError: module ‘asyncio’ has no attribute ‘WindowsSelectorEventLoopPolicy’

This only happens when I want to open a notebook in the new environment. I already created another environment a few weeks ago and that seemed to work fine. However, then I deleted that environment and when I wanted to create a new one, it wouldn’t work anymore.

I work with Python 3.6 and Tornado 6.0.3

What can I do about this?
Thank you in advance!