This issue occurs when you enable a URL filter to block URLs that contain file type extensions in Microsoft Lync Server 2013 Control Panel. It occurs because the extension of the file in a URL is not checked when the URL does not contain the "http://" prefix.
This issue may occur on hyperlinks that resemble the following:
www.abc.com/app.exe
Resolution
To resolve this issue, install the May 2015 cumulative update for Lync Server 2013 (Front End Server and Edge Server).
