GIRAUDEAU-BOCQUET, LIONEL:
The write part went fine too, and the blade rebooted properly with the latest Bios version.
Second blade's flash try was different. It uses a AT25DF641(A) chip instead of a AT25DF321. The image size is 8MB instead of 4MB.
Double-check there isn't a separate Bios available for download for this blade variant. Flashrom should work then. I'm pretty sure different sized flash needs differently packaged firmware, but am not the expert by any means.