After Speedtree import Rebuild Light source failed


I have compiled Unreal 4.3 for OSX Marvericks 10.9.4 After importing a Speedtree .srt file (no problems ) and putting the tree in my scene i get a warning tha lightining need to be rebuild but after doing that i get Lighning build failed “Swarm failed to kickoff” Any idea what happend ?
Thank you in advance for your help !