The extension is not compatible with Dreamweaver CS3 as the system requirements for the extension mentions, so I think that you should contact sales (sales AT webassist DOT com ) for a refund if you don't have access to Dreamweaver CS4 or above.
As I worked on the extension I should have added a restriction in the MXP installer to make sure that it couldn't be installed into earlier versions of Dreamweaver. I'm sorry about that.