Let's add this to the list of Google bugs we have been reporting about in the past week or so. A Google Maps Help thread has confirmed reports from Google that their "print" button on Google Maps is not working for all users.
First reports came in in late January and yet it still seems not to be fixed. On February 5th, a Google Employee, Alvin, confirmed the issue reported by a user:
I heard from Google that they have escalated this problem to their engineering team and are working in a fix.
In the meantime you will have to keep using the workaround described by others in this thread to print the directions. The main limitation is the loss of the ability to customize the print out.
This seems to be a frustrating issue for many Google Map users. The issue does not yet seem to be resolved and we have no estimate time for when it will be fixed.
Forum discussion at Google Maps Help.