What does !slot->GetLocalAABB().IsValid() mean?

I get the following message on my editor log:

!slot->GetLocalAABB().IsValid()
UnityEditor.EditorGUIUtility:RenderGameViewCameras(Rect, Rect, Boolean, Boolean)

This happens when I select a GameObject (it's a particle system) in the editor.

This message is an assert from Unity. It is basically saying that an AABB (axis aligned bounding box) for a game object is not valid and it is meant to be valid. AABBs are used in Unity to help decide whether objects are visible in the camera - they are boxes that fully enclose the object. (Think of them as the smallest cardboard box that the object will fit into with the box aligned to the XYZ axes. Normally AABBs are managed automatically for you; Unity can look at the vertices of the game object and figure out the AABB. For dynamic objects, such as particle systems the bounding box can end up being infinitely small or infinitely large, and these situations render the AABB as invalid, which triggers the assert.

If you get this assert with particle systems you can probably ignore it - perhaps the initial positions of the particles are all at the same point in space so the AABB is infinitely small. If you get this assert with other game objects it may mean something is wrong with the vertex positions.

Min/Max Emission and Min/Max Energy had to be at least 1 for me to fix this one.

i'm experience the same problem, altough bit different, i set my particle emit range below 0, and i get some error but it doesn't effect my game anything.

i change it again to 0 and the error gone :)