I did try last (1.6.13), the previous (1.6.12), same warning.
I did try the 1.6.0 and won't compile the RF24 library.
Now downloading the 1.6.5.
Do you have some hint on which version? If I try to load a bootloader and sketch, there will be error or is it only a warning?
(with Arduino UNO no problem with loading sketchs).
Thank you