Article ID: 2880163 - View products that this article applies to.
When you sign in to Microsoft Lync 2013, a proxy authentication dialog box appears unexpectedly. This issue usually occurs when Lync 2013 tries to connect to a proxy server to download an external picture for an external contact. This issue may also occur when the external network has a proxy server even though the local network doesn’t have a proxy server.
To resolve this issue, install the following update:
(http://support.microsoft.com/kb/2825630/ )Description of the Lync 2013 update: September 20, 2013