Flight Question Jupiter III-X CTD

[Kaito]

So, i'm trying to learn to fly Staged Vehicles. I downloaded and installed the Jupiter III add-on, and I got it into orbit on the second stage. But i still have 15.6% fuel remaining, so i decided to press J to jettison it. Well, doing that crashed me. It also happens with the Nova rockets.

Whats going on here?

EDIT:
Nevermind, I forgot to install the last stage of it. Fixed

 

[Alexander19851]

Um i was wanderring where did you find the addon because i'm looking for the addons for vertical launches from top to bottom.