Google made an update in their extension installation process which prevents extensions from other websites than AppStore to be installed...

An update in google chrome will allow you to parameter a white list of websites which can install extension... until then, follow one of these steps

• Secure way : Click here to download latest AMR version. Go to chrome://chrome/extensions/ (Extension page) and drop the file you downloaded there. This will install AMR !
• ...or...Add a parameter to chrome start : right click on your google chrome icon and click on properties. On the target field, after ...chrome.exe", add --enable-easy-off-store-extension-install and restart chrome. All websites will be able to install extension.