Open Dreamweaver and then go to Commands -> Manage Extensions to open the extension manager. once the extension manager is open, close Dreamweaver.
I have seen instances before where installing the extensions by double clicking the MXP File to start the extension manager does not work properly, in some instances you need to open the extension manager through the DW Commands menu to get it to work correctly
uninstall each of the extensions, then reinstall them by clicking the Install button in the extension manager and browsing to the MXP File you downloaded.
install the extensions using the following order:
Also, if you have an Anti Virus package like MacAffee that contains a real time file scanner, you should disable that.