Unfortunately this sounds like a Dreamweaver issue that would have to be taken up with Adobe support. Nobody else has reported this problem yet, but the fact that it installs on your admin account implies it could be some sort of permissions or installation problem with Dreamweaver itself.
I couldnt' find record of that error message anywhere in our forums or on the web, so it must be pretty unique to your configuration. I don't think there is anything wrong with the extension itself causing this particular problem. You may just want to install extensions as administrator in the time being to get around the issue.