Hi,
As a general rule, it's always very important when unpacking any libraries for "catalogue use", to leave its folder structure as it is (it should be unpacked with its full folder structure).
In case of HD Flowers 3, select the hd_flowers_3 folder as a library path and this should contain 3d-models-mentalray & 3d-models-vray to work properly (as on attached screenshots). Otherwise it'll not recognize corresponding path to scene file(s).
Best regards,