What version of Dreamweaver are you running? How are you installing DataAssist? In DW CC 2015 the adobe extension manager won't work, so I've been suggesting the DWMX Zone one: http://www.dmxzone.com/go/22670/dmxzone-extension-manager-for-dreamweaver
If your installation isn't working, then give me a call and I'll help you through it, or post your phone number here and I'll call you.