Surely one can translate Iuppiter as Jupiter. Duo doesn't seem to think so - he marked me wrong!
Oh, it just occurred to me: this looks like an English-to-Latin translation. You normally can't use anglicized spellings like "Jupiter" in the Latin translations, just as you can't change "Stephanus" to "Stephen" and expect it to work.
Report this one, then -- I've normally been able to use Iuppiter and Jupiter interchangeably, at least in the English translations.