After reviewing the source code again, i have not found any bug and all tests works fine for me, so i think this issue may be a network problem. As you can can see in the dialog, Max finds the bitmap in the map paths (and it even shows a preview !).
Please, use the attached ForestPro.dlo. This release retries to load the bitmap three times before displaying the error message, that may help if there is a network problem.
All the distribution bitmaps are in 3 places:
1. In the 3dsmax8\plugcfg folder
2. In a folder C:\ForestPro_maps
3. In the project maps folder
Copy them also in the same path of the plugcfg folder used to edit the scene. For example, if the computer where you created the scene has the maps in c:\3dsmax8\plugcfg, create this folder in the slave stations and copy the maps there. By default, Max (and Forest) tries to load the file with the original path (as c:\3dsmax8\plugcfg\dense.bmp), and if it doesn't exists then searchs in the map paths.
However, try this only if the modified plugin fails too (i like to know if it fixes the problem).
One thing I notice, when I use the 'Bitmap/Photometric Paths' utility to edit all the map paths in the project to make sure they're UNC, the maps used by ForestPro do not show up there. Seems like they should since they are a map like the others.
That is the expected behaviour. This tool only works with materials and textures, not with the custom bitmaps used by the plugins.