Can't save a custom OBJ to the library anymore

Hi there! I have a questions regarding custom 3d files.
I been working on a couple of files for a product for a while now, the 3D model I been working have had iterations on the last couple of months. I have some of the previous OBJ files for this product saved on my library but I'm unable to add new ones, can't copy paste them either from a new file.
How can I add a new custome obj file to a scene? I used to just saved it to my library and add it to my scene. But now everytime I tried to drop the file on the library I got a message saying the file is not supported but it is! I have previous versions of it. 

I'm worried I may have to re create huge scenes from zero everytime I have to a new iteration. Am I doing something wrong or there is a new way to add custome objects to our libraries?

Thanks in advance!