ransomryan111 wrote:
when the computer arrived, OS X was not installed. when i attempted to power on the computer, i came to a grey screen with the "prohibited" symbol (like the ghost busters 🙂). so i restarted it in recovery/repair. then under OS X Utilities, i selected reinstall OS X (reinstall a new copy of OS X). the next window says OS X El Capitan: To set up the installation of OS X 10.11 click continue. Next it verifies my eligibilty and asks me to agree terms. Next i tell it to install on Macintosh HD, as that is my only option (Recovery HD is locked). I click install and am asked to sign in to download from the App Store. Here is where I get the same unexpected error message. So now I'm stuck.
Yeah, as I said, the original owner didn't do what they were supposed to do. Before selling you the computer, they were supposed to reinstall the operating system themselves. It sounds like the computer wants the original owner's Apple ID and password, and since you don't have it, it won't let you proceed. You need to find a way to get in contact with the person who sold it to you, possibly arranging for you to mail it back so they can take care of what they needed to take care of.
What to do before selling or giving away your Mac - Apple Support