DESIGN EXTENDER 1.1.8
does this mean you have the stand alone extensions installed along side Data Bridge and Design Extender? if this is the case, that will be the cause of the problem. You should only have Data Bridge and design Extender installed, not any of the stand alone extensions.
after installing Design Extender and Data Bridge in the extension manager, you will need to Open Dreamweaver to start the webassist installer which will complete the installation. If the webassist installer does not open automatically, try opening a php page, that should trigger it to launch. Once the webassist installer completes, make sure to restart DW.