Terrain Painting/Editing glitch

Hello,

Have tried googling and otherwise looking for an answer to this, but have come up empty.

I'm having a problem with TGE wherein, after a while - and I'm not sure what variety of steps/actions - when I go into Terrain Paint or Terrain Edit mode, the brush does not appear, and I'm unable to do either. I've tried saving the mission, closing and re-opening it, and it still won't work.

I'm sure this isn't something new, and there's probably some way to fix it... but I'm not aware of it.

Can anyone shed some light on this?

If it helps any, the only thing I was doing prior to this was editing the water block settings to play around and see what I could do. Was actually trying to figure out how to make underwater look foggier/murkier than it does.

Any help is appreciated..

Thanks!