After fresh Skype for Business 2015 frontend pool installation, I was not able to start RTCSRV service, I tried different things and I ended up reseting pool with command Reset-CsPoolRegistrarState. Command failed with following error:
After some troubleshooting I noticed that I forgot to install latest Cumulative Update.
I downloaded Skype Server Update installer from:
followed following guideline:
and installed CU on all FrontEnd servers.
After reboot all CS services started successfully.