Sadly this bookmarklet longer works thanks to pivotal hiding their JavaScript code and blocking clients from using the API from their own domain..
You might instead like to look at one of server-side versions of this project such as card-omatic (JordanHatch/card-o-matic) or bewt85/print-pivotal-cards.
It was nice while it lasted ..
Printable index cards for your Pivotal Tracker project.