Custom Data Connectors issue "Failed to edit credentials"

Hi,

I am trying to get started with Custom data connectors
But I can not run even the basic demo , I get "Credentials are required to connect ..."
There is no "Add Credentials" button on the M Query output windows.
When i press Edit Credentials i get :
"Failed To edit credentials
Details:
Object Reference not set to an instance of an object"

Any idea ?

Thanks !