http://blogs.msdn.com/b/pareshj/archive/2012/12/04/lync-desktop-sharing-fails-when-one-user-is-internal-and-one-is-external-in-your-network.aspxHad a customer recently report that they weren't able to perform desktop sharing with their clients outside of their corporate firewall. Looking at the reports showed this error ms-client-diagnostics: 24; reason= "Call failed to establish due toen-GBTelligent Evolution Platform Developer Build (Build: 5.6.50428.7875)http://blogs.msdn.com/b/pareshj/archive/2012/12/04/lync-desktop-sharing-fails-when-one-user-is-internal-and-one-is-external-in-your-network.aspx#10415668Thu, 02 May 2013 15:19:37 GMT91d46819-8472-40ad-a661-2c78acb4018c:10415668NetworkCarpenter<p>We are running into the same issue and are in fact running Kaspersky AV. Could you provide any details as to what tweaks you made to Kaspersky to get this working?</p> <div style="clear:both;"></div><img src="http://blogs.msdn.com/aggbug.aspx?PostID=10415668" width="1" height="1">