Kindlegen 1.2 issue

I’m attempting to compile a .mobi book.
(note: This worked fine on my previous machine, a G5. On my new iMac…not.)

I’ve twice downloaded the everlovin’ Kindlegen zip file for Mac, v. 1.2. The first time, I attempted to run their “instructive” insert command line process to no avail–at least on my Terminal, it did not play.
In any case, that said, when I attempt to compile, I get an “Invalid KindleGen file” message: “The file at /users/me/desktop/ does not seem to be a valid KindleGen file. Please try re-downloading and re-installing Kindlegen.”

So…have redownloaded, but I have a feeling there’s something funky with the “install” portion of the program. Very likely pilot error, but I am at a loss. Any advice?