I have been consistently getting this error message upon loading into a new save, without any other mods installed:
Error extending trajectory for Laythe. Error trying to fit a smooth polynomial to the trajectory. The approximation error jumped from +2.30344324226492217e-03 m to +8.35706270893752298e+03 m at time 2000-01-19T18:40:00,0000000000000000 (TT). The last position is [+2.82771976953634682e+10 m, +5.89455954369199753e+10 m, +3.17994282982390106e+08 m] and the last velocity is [-3.61414693067490953e+03 m s^-1, -1.47464668046310658e+03 m s^-1, +9.66125813160947615e+01 m s^-1]. An apocalypse occurred and two celestials probably collided because your solar system is unstable.
I believed that Principia altered the stock system to create stability, and now I'm confused. Vall has been ejected from the Jool System and is now orbiting the sun in a highly elliptical pattern.
Please help
Edit: In addition to other wild bugs, (terrain being reshaped, causing kerbin to be unrecognizable, none of the celestials progressing in their orbit, etc.,) the problems were isolated to the singular save I had created. I did have Kopernicus in the game directory when I made it. I'm a derp.