Archicad manages a complex database that interferes with adding content, like textures.
To register a folder in Archicad's library, use the Library Manager to locate and load it into the library. From then on that folder is included when you load the project.
Texture images can be dragged into the existing library, but for Archicad to see the data, you must reload the entire library in the Library Manager.
A way to avoid this time-consuming process is to make a bunch of dummy files as placeholders in the library and simply paste your new texture into one of them. The address is loaded already, so you can immediately begin work.
Dwight Atkinson