I I can't launch the jupter notebook from anaconda navigator

Getting Started
1

I can’t launch the Jupter notebook from Anaconda Navigator, although I was able to do so yesterday. I got the following message:

 Sorry, this is not working properly!

Our server encountered an unexpected condition that prevented it from fulfilling your request.

Internal Server Error

Failed to connect to Hub API at 'http://127.0.0.1:8081/jupyterhub/hub/api'. Is the Hub accessible at this URL (from host: green-nbjupyterhub12)? Make sure to set c.JupyterHub.hub_ip to an IP accessible to single-user servers if the servers are not on the same host as the Hub.
2

I tried again and was able to launch Jupyter Notebook from the Anaconda navigator, but the other problem occurred: the kernel selection dialogue box did not allow me to select any kernel.

3

Now the Jupyter Notebook can be started, the kernel can be selected, and all of its functionality has been restored.