The Library Browser (with Evermotion Catalog add-on istalled) is looking for the "original folder structure" after unpacking. Please unpack all assets (textures & models) with their original folder names into one "parent folder" (maybe that could lead to these troubles as their models are delivered "by folder"). Than you should map the "parent folder" - containing Textures (maps) folder and your renderer's folder with models (Vray, MentalRay, ScanLine). Also please note, you shouldn't rename these folders (as our add-on uses that original folder names to allocate corresponding .max files for selected renderer).
As our "installation checker" is looking for the first MentalRay model file, the "MentalRay" folder should be unpacked also. Could be, that you didn't unpack that folder? If so, please unpack it (also in case you'll be not using this renderer).
Than, when EvermotionPlants Libraries pop-up window asks you to Select Installation Path you should select the path to whole folder structure (not where corresponding models or textures are located). It should be the folder where you have extracted all these assets (including Textures (maps), MentalRay, Vray and ScanLine folders).
It´s strongly recommended to include the Textures (maos) folder into your User Paths. This way, bitmaps are always found when loading or importing models from the library. The path to your location of used assets should be added to the 3ds Max configuration by using Customize - Configure User Paths - External files.