Well, i just done a test in a Max configuration without VRay:
- The HQ Plants max files include the VRay materials in the material editor. This is the reason to get the missing VRay error when importing the trees from the library.
- Using the Merge mode, the trees are merged in the scene and Forest applies to them the Mental Ray material. If the scene is saved, there is not any reference to VRay.
- But using the XRef mode, we create a reference to the HQ Plants max file. Since this file uses VRay (because the material editor), we get an error each time the scene is loaded or rendered.
Unfortunately there is not an easy solution to this issue, because we cannot modify the HQ Plant files from Forest. Perhaps you would to leave installed the VRay demo to avoid the warning messages...