Hello, I've just tried to update firmware of my Expansion Board v3.0 and faced the same issue. Does anyone knows how to fix it? Thanks in advance, w

@paul-thornton The timing is rather critical. Couldn't you extend the time window for updating to let's say 30s?

I came across this "bytesdfu-util: Error sending completion packet" error today when attempting to upgrade a Pycom Expansionboard 3.1 connected to an Ubuntu 18.04 LTS. Running ls -la /dev showed that the serialport had restricted access, so a quick fix was: sudoedit /etc/udev/rules.d/50-myusb.rules and insert the following: KERNEL=="ttyUSB[0-9]*",MODE="0666" KERNEL=="ttyACM[0-9]*",MODE="0666" then sudo reboot After rebooting the firmware upgrade worked great (holding the s1 button when connecting the USB-cable; releasing s1 after one second; then running dfu-util within a few seconds). sudo su - dfu-util -D /home/user/Download/expansion31_0.0.11.dfu

@tealbrains & @Xykon : thanks all , that was that ! sudo dfu-util -D ./expansion3_0.0.9.dfu -R -v (I had added my user to dialout group already : not enought)

Thanks for this information. Aparently I misunderstood documentation all those names are confusing at begining.