Hello Alexey,
The step that failed was the photo orthorectification in the orthomosaic generation. I think that my mistake was to change the coordinate system (WGS 84 to WGS 84 UTM zone 20, in my case) at the orthomosaic step. Thus, I change the coordinate system at the DEM generation step and it worked perfectly. I tried the same process with an other data set in RGF 93 and it worked well too.