Criminal Law Questions? Ask a Criminal Lawyer.
No the ticket is not invalid, however you will need to call the telephone number on the ticket and get the correct hearing date scheduled. Unfortunately if you don't show up for your ticket then a warrant can be issued for your arrest, so it is in your best interests to figure out when and where your hearing is.
Cops and courts make mistakes all of the time, however you don't want to have to go to jail just because a clerk put the incorrect date for a hearing on your information. Good luck!