Same problem, just upgraded to 10.9.5 and I can't get my Mac to recognize my HD500. I have uninstalled and reinstalled Monkey, Edit, Workbench, you name it and nothing i do gets my machine to install 7.3.6. it always shows up as an update on Monkey and won't install no matter what. I know the problem is not with the USBs or cables because I use them for other things just fine. This is so frustrating; I have support ticket out to Line 6 and they haven;t been helpful as of yet.