FC1888 is correct. Folders must be in the External files dialog list.
The list can be populated by ForestPack plugin automatically.
Most likely OP disabled this function in previously.
Please check this folder if it has Your mentioned files:
%localappdata%\Itoo Software\Forest Pack Pro\lib\Presets\Layered_Lawns\maps
If it does not You will need to redownload assets using update manager.
If it does then all right, proceed with further information below:
Please check this thread
how to reenable feature that collects folders to "External Files list".