Russ,
This error is typically due to a problem with Dreamweaver's Cache file.
See the steps here to fix: 146/
Adobe has promised to fix this issue going forward in CS5 but until then, I have just made it habit of deleting the Dreamweaver cache file after installing any new extension.
I can almost guarantee that the extension is totally fine and will work great after you take the steps from that link.
Best regards,
Brian