That is the latest version that the software for my piece of scientific equipment would run on; after that they stopped supporting Macintosh versions of their software. I build an old PC running Windows 7 but the damn thing is (a) so foreign to me and (b) the screen images of what I need (I’m taking photomicrographs of tissue samples) are not what ends up as the camera shot.
Bob
Hi Fritz
Did you download the installer from Apple or a third party site ?
From Apple
From the Mac App Store
IIRC, I noticed that its modification date was the same as the original installer I had saved, which I found curious.
Is your Mac Pro on the list of compatible Macs for Sierra? You haven’t told us what model/year your Mac Pro is. My old cheese grader Mac Pro topped out at Lion. There are a few newer models that could go a bit further. The page explaining how to download macOS 10.12 Sierra, https://support.apple.com/en-us/HT208202, lists Mac Pros from mid 2010 or later as compatible. If yours is earlier than that, it explains your problem. If it’s a mid 2010 or later, then you have an issue. Since you are trying to install a supported version of macOS, Apple Help may be willing to assist you, 1-800-275-2273. You’ll need your Mac’s serial number to get that assistance. See About this Mac in the Apple menu.