TPKD is the iLok driver file. Pro Tools needs this driver to be properly installed and free of conflicts in order to work. To get rid of this error, try the following:

• Download and install the latest drivers from http://www.paceap.com.
• Uninstall Microsoft Outlook. Outlook has been known to conflict with the iLok drivers and repeatedly give this error.
• If this still doesn't help, uninstall and then reinstall both pro tools and the iLok drivers.