Ok, i just realized of the problem: the library has the material path hard coded to C:\Program Files (x86)\Itoo Software\Forest Pack Pro\matlib, but this folder is valid only for Windows 64 bit, not Win 32.
Please, overwrite the XML files of C:\Program Files\Itoo Software\Forest Pack Pro\lib with the content of the attached file. That should solve the problem.
We will included this fix in the next patch as well. I apologize by the inconveniences.