RSS/RP1 Orbital Rocket Problems

[jopun]

RSS/RP-1 has been a really fun and enjoying experience, and has brought a bundle of new challenges and idea ahead of me, but my latest mission has not went as planned. After around 10 sounding rockets, I finally had enough science to attempt orbit, and I did so by copying YouTubers Carnasa's beginner orbital rocket design. It works perfectly, and MechJeb has helped me fly it, but the last stage has completely flopped. The final stage is an uncontrollable rocket with the aerobee engine, the tank is pressurized and has enough Delta V to get my periapsis to 140 km, but when I try to ignite the engine, a prompt with the text "Insufficient avionics 0.000t out of 0.625t supported." In my previous uncontrollable rockets this wasn't and issue, and they flew perfectly fine without this prompt. For some reason however, this stage of this specific rocket is causing problems. https://imgur.com/gallery/jdp7c9U (this picture might help )  

My probe is set to Avionics Prototype and Scientific - Core, and in Carnasa's video, the prompt popped up on the screen but the engine still fired up. Is there anything specific I may need to try or add? I will give any other required information to solve this problem,

Sincerely,

A Kerbonaut In Peril.

[Xt007]

If you don't specify a controlled weight or use a probe core with a controllable weight.  When you're in vacuum there are no other forces (air, gravity along axis of thrust) to keep the craft stable

[Xt007]

Second issue, ulage.  Either ignite the aerobee before separation or you'll need kick motors or rcs.