As Mr L says, MPC is years old and has been abandoned by Amazon and apparently by Mobi itself. I recently got a PayPal payment for my Mobi books (four years' worth, tee hee) and I took that as a signal that they have closed down the operation.
It's supposed to have been replaced by Kindlegen, but I've never managed to get that working. I upload html files (zipped with the images if any) then download the converted mobi file and check it out in the excellent "enhanced previewer." Takes only a few minutes.
As I understand it, KF7 formatting is a direct descendant of Mobi, but KF8 (for the Fire etc) is a whole new thing. The disadvantage of being the big first mover is that you get stuck with the legacy system. Sony chose to switch to epub, but Amazon did not, and it has too much invested in Kindle Format to change now. It's a bit like VHS and Betamax. Betamax was the better format IMHO, but VHS wiped it out. Epub is the better format, or so many argue, but Kindle rules.