Update that reverts the Application Sharing Server (ASMCU) changes in CU4 in Skype for Business Server 2015 Content provided by Microsoft Applies to: Skype for Business Server 2015 Select Product Version All Products Symptoms You receive a RTP and RCTP muxing issue after you upgrade the version of Microsoft Skype for Business Server 2015 to cumulative update 4 (CU4). Resolution To fix this issue, install the February 2017 cumulative update 6.0.9319.277 for Skype for Business Server 2015, Conferencing Server. Last Updated: Mar 24, 2017 Did this solve your problem? Yes No Tell us what we can do to improve the article Submit Thanks! Your feedback will help us improve the support experience.