At some poinet, the bluetooth in my MacBook Air could not be activated any more. The commands that helped were

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.blued.plist

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.blued.plist

Thanks to Macuser.de

A simple script to aid in this situation:

#! /bin/sh

case "$1" in 
"start")
      launchctl load -w /System/Library/LaunchDaemons/com.apple.blued.plist
      ;;
"stop")
      launchctl unload -w /System/Library/LaunchDaemons/com.apple.blued.plist
      ;;
"restart"|"reload"|"relaunch")
      "$0" stop
      "$0" start
      ;;
*)    echo ERROR >&2
      ;;
esac

OSX Bluetooth