I tried to download the XFrogPlants Catalog as well, but the application works in conjunction with the Forest Pack Lite. I've been redirected to the page with the program, but it appears that I need 3Ds Max.
Firstly, make sure that you have Forest Pack from the following website:
https://www.itoosoft.com/freeaddons
Afterward, start the software to browse the catalog and follow the instructions presented in the Help file.