Make sure that you have the DW 8.0.2 update installed. this should be installed before installing any of the extensions. if you don't have that update installed, uninstall the extensions, instal the update, then reinstall the extensions.
the update is available for download from the Adobe site from this page:
more information about the updates is here:
Just FYI, Note the System requirements for DW 8, you may need to run DW 8 in compatibility mode on Windows 8.1:
Dreamweaver 8 supports Windows® 2000, Windows XP and Macintosh Mac OS® X 10.3 and 10.4. Starting with this release, however, Dreamweaver no longer supports Windows 98, Windows 2000 Server, Windows 2003 Server, or Macintosh OS 10.2.x or earlier.
Complete product system requirements and recommendations are available at www.adobe.com/go/sysreqs.
This product contains activation. An Internet connection is required to complete activation.