After rebooting one on my XenApp servers the other day I was then unable to log on receiving the error “The Local Session Manager service failed the logon. The requested session access is denied”
After some investigation the local session manager was failing to contact the Windows license server. The server was up but the Remote Desktop Licensing Manager was showing as “Not Activated”, clicking activate just resulted in a further error. The event manager was also showing the following.
After some more search I discovered a Microsoft KB article KB983385, it turns out an expired certificate was causing the issue, after installing the hotfix and rebooting the license server I also had to reboot the XenApp server at which point I was then able to log on again.