Sounds like the web Assist installer did not open to finish the installation.
after installing the extensions, when you open DW, it should launch theWebAssist installer to complete the installation.
if the WebAssist installer does not open automatically, open a php page to force it to launch.
Try uninstalling the extensions, then installing them again.
and make sure the WA installer opens when you open DW. after the WebAssist installer completes, make sure to restart DW.