Due to recent changes in Google security policy Chrome extensions can only be installed from Chrome Web Store by default.
We are working on a permanent solution. So far following workarounds are available:

• Manual Installation
  • Open a new tab and type chrome://extensions into the address bar
  • Drag and drop the extension file onto the tab
  • Confirm adding the extension
  • Update this page
• Allowing non-Web Store installation locally
  • Run Chrome with --enable-easy-off-store-extension-install command line key
• Allowing non-Web Store installation via domain policy
  • Import LegaSuite domain policy templates from [J Walk CD]\Tools\Administration\legasuite.adm
  • Enable the "Allow Google Chrome to install extensions from the listed hosts" policy
  • Add GUI Engine host name(s) to the list
  • Apply the policy

Please refer to J Walk documentation for more detail.