It is possible that the hard drive in question is in a format that can be read but not written to with the Mac OS. I ran into that problem with a 1TB drive, I ran it on my PC Laptop first and then plugged it into my MacBook Pro, and I could see and read the files but could not write to the drive. Luckily, it was a new drive and I just reformatted it, plugged it into the MacBook Pro first, and then into the PC Laptop and now it works on both, my recommendation, save everything on the external drive to a different drive, reformat the external, plug it into the MacBook Pro, and then copy everything back to the external. You should be able to save the files to the drive then. As for your Jolly Roger, check and see if the drum lights up when you hit the pad that should trigger it, if it doesn't, then EZDrummer is not receiving the MIDI signal. You may have to go into your preferences for EZDrummer and see what your MIDI input is set to. It very well may say no MIDI input device selected. I am not familiar with the Presonus so I can't be much help with that, but if you are getting sound out, it should be hooked up correctly. This may sound dumb, but check to make sure you are plugged into the MIDI in and not the MIDI out, I have done that by mistake. Maybe we can Skype later tonight and try to work it out. My Skype address is pocketmaster6287, maybe we can work this out.