I have a problem with Library Object in Archicad, mate. :)
Can you put them to Embedded Library?
Seems like this is not a Corona Renderer related question, and as far I understand your issue, I suggest to ask for help rather on the ArchiCAD developers ( Graphisoft ) forum.
Actually it could be (a Corona related question not necessarily directly connected to ArchiCAD).
It's one that's come up before in a different way.
Right now, the Corona plugin gets its textures (maps) information from the ArchiCAD material setting (and loaded maps in the library), which means that if your maps are or were saved as part of the embedded library (or as an ArchiCAD archive file (PLA) with all the library information embedded in) then it will (presumably) get the texture information from that.
But there was talk ( I can't remember if here or at the ArchiCAD forum) about the possibility of loading or saving Corona proxy objects with the ArchiCAD library once the Corona proxy library object issues were fixed or sorted out.
The Corona proxy object is loaded as a library object which then references an external file (like an OBJ file or a Corona format proxy object (GEO).
Is, or can the assumption therefore be that if I had an ArchiCAD file set up to render with the Corona plugin and had some Corona proxy objects (like trees or furniture, for example) as part of the setup, and then saved the ArchiCAD file as a PLA or with the loaded library objects embedded, that the Corona proxy objects (which would read to ArchiCAD as plain simple geometry objects like simple cubes or planes) could also be conceivably saved along with all the other library objects?
I suppose some cross-checking would be necessary upon loading the file to make sure the paths to the actual proxy files or objects were correct - unless these could also be set up to read as relative (as opposed to absolute) paths like some ArchiCAD reference objects and documents.
I'm not sure if you understand how I mean it.