It sounds lim the extension manager installation has become corrupted.
I would try uninstalling Dreamweaver completely, and uninstalling the extension manager.
after uninstalling, delete the users configuration folder for both the extension manager and dreamweaver. depending on your OS, there may be an adobe utility for uninstalling. you should look through the adobe forums for details on uninstalling Dreamweaver and the extension manager.
A fresh install should fix the problem.