This is the relevant part in step 2:
"The error message "Menu cannot be updated, the extension cannot be installed" is caused by a bug in Dreamweaver where the menu.xml file can sometimes become corrupted. Performing this step should clear the error."
Ah, I see it now.
This is ridiculous though!! I have to uninstall ALL extensions and re-install them? I really can't think of anything better to do with my time... *sigh*
What I wonder though is; that the page states it is "Dreamweavers fault" - I was able to install another WA extension afterwards. What sense does that make? Either the config file is corrupted and affects all extensions that one wants to install - or it's not the config file but the extensions "fault".