Apparently something has changed with 10.9 in AirPlay mirroring, so when Syphon Virtual Screen is installed Airplay mirroring is broken. When selected it does not activate and an error is reported in the Console log. Other apps using virtual frame buffers are affected (AirParrot, AirServer). See this discussion:
To fix this issue just delete the frame buffer (/System/Library/Extensions/EWProxyFrameBuffer.kext) and the kext cache folder (/System/Library/Caches/com.apple.kext.caches), then reboot.
👍 thanks I had big laggs in my editor Atom and removing these files worked for me!