Thank you very much Steveps3 ! It works with Blender 2.69 for Octane. Not yet tried with 2.70 For octane, as I have not yet installed it . I would have to deinstall the current version but I don't want to do it right now in the middle of a project.
However : your modified v0.1.9a version doesn't display the export obj/mtl button, but exports directly the obj and mtl. It is fine for simple objects, but maybe it would slow down the export for complex objects. Also, there is the risk of overwriting obj file previously exported with the unofficial obj exporter. So, a button offering the choice of exporting or not the obj/mtl like previously would be safer imho...
Even no button and so no export at all of obj and mtl would be fine, as this can be done in a safer way with the obj exporter itself.
I spent hours searching how to disable the export of obj and mtl, but as I said in some posts , I have no skill in coding, and the only thing I have been able to do so far is to change the commentaries in the GUI to show 1.0.9a as version number to avoid confusion !
EDIT : I tried with logic and trials and errors, and finally I disabled some lines and the Obj and Mtl are no more exported. However, I don't know if they are internally computed and if some ressource is wasted in the process. I have to test with a big Mesh as instance.
Below the modified script and a screen shot of the disabled lines in the script. Please could you tell me if I did it correctly ?
French Blender user - CPU : intel Quad QX9650 at 3GHz - 8GB of RAM - Windows 7 Pro 64 bits. Display GPU : GeForce GTX 480 (2 Samsung 2443BW-1920x1600 monitors). External GPUs : two EVGA GTX 580 3GB in a Cubix GPU-Xpander Pro 2. NVidia Driver : 368.22.