Maneuver Nodes Not Working

[Dukemaster]

I'm using Realism Overhaul and RP-0, along with a whole host of other mods for this playthrough. I do have Mission Control and the Tracking Station upgraded to level 2. Yet for some reason maneuver nodes are unavailable to me. For a brief time while ascending through the atmosphere I can click on my blue line flightpath and place a node, but once I get high enough and transition to space, my flightpath line turns pink and I can no longer click on it. Also, I cannot right-click on other ships, moons, or planets to make them targets. I can't rendezvous with anything, or leave Earth orbit. Essentially, I can't play the game.

I'm not sure if this is MechJeb, Principia, or some other mod that's blocking it, or perhaps a setting I haven't found yet, or a genuine bug.

Please help. Many thanks and appreciation to you all.