Lyne, of course, you can populate the old Vue5 way, and it is done exactly the same way, in the material editor, you check the ecosystem button, and then you have the general, density, etc etc tabs. If it doesn't populate, there are 2 reasons that come to my mind:

• you have foreign objects in the scene and your "decay near foreign objects" is too strong ( it 5% by default), so change this value or make foreign objects eco friendly by clicking the tiny plant icon under their material preview in the object manager.
• the terrain you want to populate on is too small, or the plants too big. Since Vue6 works in real world measurements, this is something that can happen more often than it used to. Check the size of your plants/terrains in the object manager, and either enlarge the terrain, or change the size of instances in the general tab of the ecosystem material. You can also change size of instances in the "scaling & orientation"tab of te ecosystem material.
  Now about ecopainting, you'll notice that the size of instances is 1.000 by default and it is way too big most of the times. You should reduce this value to 0.500 and see if it is better. If not, clear the population and change the value again before painting.
  Don't give up on 6, Lyne, it may take a while, but you're gonna love it.