Not sure how that would happen. Did you do a System Restore or install Photoshop or Premier or Elements? Have you tried downloading and installing the update, again, from http://www.adobe.com/downloads/updates/
Did none of the mentioned, i.e. System Restore, or install any of the programmed software. Today I uninstalled my old DNG converter and will see if 6.4 stays in place.
I did none of the mentioned items. Today I uninstalled the DNG converter and then installed the new one --6.4. We will see.