I have the same issue with "Too heavy: Bring more kerbal [*Object Mass Here* > 0.000t]", after having just installed KIS version 1.2.8 from curse.
Steps to reproduce
1. Build basic rovercar in free play mode.
2. Add a couple of basic tools and components with near no mass (eg. ground pylon) to the pilots inventory.
3. Deploy to runway
4. EVA and get on the ground
5. Open inventory and try to drag ground pylon or other part out into the world.
Result: Error message pops up.
I tried taking a vanilla unmodded KSP 1.1.2 and installing KIS & KAS in their freshly released versions (from curse) into that installation. In this case there was no problem, it works and i can attach a ground pylon to the surface of Kerbin with no error message appearing when i drag it out of the inventory.
So i went problem hunting. Turns out that for me it's caused by combining KIS/KAS with TweakScale
As soon as i added KIS/KAS and TweakScale to the vanilla copy of KSP 1.1.2 the problem pops up. I have a long mod list so i dont know if other things than tweakscale causes issues, but for me KIS/KAS & TweakScale do not seem to play well together.
Any chance for an update to KIS/KAS that'll fix it so it'll play nice with TweakScale? Or is it more likely that the problem lies in TweakScale itself?
I imagine that since TweakScale can dynamically scale items (including mass and such) up and down the issue may stem from something to do with this? (I'm guessing here though, i have no insight into the inner workings of TweakScale).
I'd hate to have to give up either KIS/KAS or TweakScale as both of them are quite important for the playthrough i have in mind with 1.1
