This error means that your ipython laptop server is not running. If you are using Ubuntu or OSX, you need to go to the cd command line in the directory where your laptop file is located and run ipython notebook. This will launch the web server of the local laptop, and you will be able to run the code inside your laptops. The error you get probably means that you accidentally killed a local web server that allows you to run laptops.
mprat source
share