I just bought a new Seagate External HD to free up some space on my mac and macbook. I installed it on my mac and then tried to move files from the macbook onto it but get a message saying I can't modify it. What am I supposed to do. SHould I install the software that came with it onto my macbook. Hopefully, I've answered my own question here. If I can't use it on multiple computers than what good is it?