The problem is that when I double-click the Lightbox MXP file the Extensions Manager opens but gives an error message: "The extension can not be installed, it requires Dreamweaver version 6.0 or later." This doesn't really make sense as I believe CS4 is version 10.
The problem may be that I have a mix of CS4 and CS5 apps on my machine and the Extensions Manager is v. 5.5. I have tried installing EM v. 4 but I can't do that as I get an error message saying it's already installed. If it is, I can't find it.