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 Was this information helpful? Yes No Tell us what we can do to improve the article Submit Thanks! Your feedback will help us improve the support experience.