try uninstalling the Extension manager from the Adobe CC Application manager, then reinstall it.
Uninstalled and reinstalled. Once installed I open a page called test.php which seems to trigger the software download from your server.
Then it just hangs for a while ( this time I left it for 10 mins ) and then it comes up with the error shown on page 2 of the attached pdf " ERROR Could not find extension on server - please try later "
Following this - Dreamweaver just hangs until I close the dialog box. This is a brand new clean Build of Windows 8 - and everything is running perfectly ( Good speed as well on Broadband )
This seems to be doing the same thing on Design Extender. I downloaded both from your server immediately before installing - no problems with Internet connection - yet it cannot seem to complete the download from your server