This issue appears on pre-release versions of Dreamweaver CS3. The extension should work on the released version (Build 3481). This is a known issue in Dreamweaver Build 3453.
Please make sure your Dreamweaver build is 3481 or greater. This has been verified and will work on working versions of CS3. To find out the build you are using go to About from the Dreamweaver menu in Dreamweaver and click once to forward to the version number and build.
If this is not the case then it is likely an issue with a corrupt config or maybe even a cache file problem.