Hello everyone,
I have been on it since two days now and I don't know what to do. Here is what I have :
pening DFU capable USB device...
Device ID 0483:df11
Device DFU version 011a
Claiming USB DFU Interface...
Setting Alternate Interface #0 ...
Determining device status...
DFU state(2) = dfuIDLE, status(0) = No error condition is present
DFU mode device DFU version 011a
Device returned transfer size 1024
DfuSe interface name: "Internal Flash "
Downloading element to address = 0x08040000, size = 119804
Erase [ ] 0% 0 bytes
Erase [ ] 0% 0 bytes
Erase [= ] 4% 5120 bytes
Erase [== ] 8% 10240 bytes
Erase [=== ] 12% 15360 bytes
Erase [==== ] 16% 19456 bytes
Erase [==== ] 17% 20480 bytes
Erase [===== ] 20% 24576 bytes
Erase [====== ] 24% 29696 bytes
Erase [======= ] 28% 33792 bytes
Erase [======== ] 32% 38912 bytes
Erase [========= ] 36% 44032 bytes
Erase [========== ] 40% 48128 bytes
Erase [=========== ] 44% 53248 bytes
Erase [============ ] 48% 58368 bytes
Erase [============= ] 52% 62464 bytes
Erase [============== ] 56% 67584 bytes
Erase [=============== ] 60% 72704 bytes
Erase [================ ] 64% 76800 bytes
Erase [================= ] 68% 81920 bytes
Erase [================== ] 72% 87040 bytes
Erase [=================== ] 76% 91136 bytes
Erase [==================== ] 80% 96256 bytes
Erase [===================== ] 84% 101376 bytes
Erase [====================== ] 88% 105472 bytes
Erase [======================= ] 92% 110592 bytes
Erase [======================== ] 96% 115712 bytes
Erase [=========================] 100% 119804 bytes
Erase done.
Download [ ] 0% 0 bytes
Download [= ] 4% 5120 bytes
Download [= ] 7% 9216 bytes
Download [== ] 8% 10240 bytes
Download [=== ] 12% 15360 bytes
Download [=== ] 14% 17408 bytes
Download [==== ] 16% 19456 bytes
Download [===== ] 20% 24576 bytes
Download [===== ] 21% 25600 bytes
Download [====== ] 24% 29696 bytes
Download [======= ] 28% 33792 bytes
Download [======== ] 32% 38912 bytes
Download [======== ] 35% 41984 bytes
Download [========= ] 36% 44032 bytes
Download [========== ] 40% 48128 bytes
Download [========== ] 41% 50176 bytes
Download [=========== ] 44% 53248 bytes
Download [=========== ] 47% 57344 bytes
Download [============ ] 48% 58368 bytes
Download [============= ] 52% 62464 bytes
Download [============= ] 54% 65536 bytes
Download [============== ] 56% 67584 bytes
Download [=============== ] 60% 72704 bytes
Download [=============== ] 61% 73728 bytes
Download [================ ] 64% 76800 bytes
Download [================= ] 68% 81920 bytes
Download [================== ] 72% 87040 bytes
Download [================== ] 75% 90112 bytes
Download [=================== ] 76% 91136 bytes
Download [==================== ] 80% 96256 bytes
Download [==================== ] 82% 98304 bytes
Download [===================== ] 84% 101376 bytes
Download [====================== ] 88% 105472 bytes
Download [====================== ] 88% 106496 bytes
Download [======================= ] 92% 110592 bytes
Download [======================= ] 95% 114688 bytes
Download [======================== ] 96% 115712 bytes
Download [=========================] 100% 119804 bytes
Download done.
File downloaded successfully
Warning: Invalid DFU suffix signature
A valid DFU suffix will be required in a future dfu-util release
Error during download get_status
Failed uploading: uploading error: exit status 74
Indeed, when I am not in DFU mode the arduino disconnects in the middle of the uploading and reconnects, so it writes the error 74. When I put it in DFU mode, there is the message you can see above.
Anyone would have an idea ? 
Thank you