Just as Daniel Gorini described, I cannot open DraftSight 2015 after a successful download / installation to my iMac running OS 10.6.8. I get the same error message and like Daniel I've deleted and downloaded DS 2015 several times, reverted to an earlier version via Time Machine backup and still get the same error message and failure to start. Perhaps this is a server / registration failure issue. When my company switched over from AutoCad to DraftSight a couple of years ago (Windows platform) I was very pleased to be able to download the Individual Mac version of DraftSight for personal use at home. Until the 2015 download I have had no trouble  with the program. I'm hopeful the problem we're experiencing will be remedied soon.