I found the answare myself.
In point nr. 3) in the email you sent me, you have written:
3) Copy libraries and textures to your 3D Studio's directories (c:\3dsmax\matlibs, c:\3dsmax\maps, etc.)
That is wrong.
I had to copy the files and folders to C:/forsetlib, because in the Bitmap Parameters, you already had linked to this path.
Now it works fine.
I also observe that the flower-materials are linked to D:ForestLib_Vol1\floverpot\bucket1.jpg
I thimk it is best to place all in C:/forestlib