For the EOS 5D MkIII

We have found that the EF 40mm 2.8 STM  firmware update failure with the EOS 5D Mark III can occur if the camera has Battery Info Registered and if the Battery Info is checked right before the firmware update is applied.

To restart the firmware update please follow the below procedure.

1.  Remove the battery from the camera and remove the lens from the body, do not remove firmware update card.

2.  Reinsert the battery and in the camera's menu go to "SET UP3" and select "Battery info."

3. When the battery info is displayed press the "INFO." button found next to the MENU button to display registered batteries and select "Delete info."
 NOTE: If "Register" is highlighted that means that no batteries are registered so you can proceed to step 5

4.  Delete all registered battery info displayed.

5.  Remove battery from camera and reattach 40mm lens

6.  Reinsert battery, "Firmware update failed. Try updating again." should appear, select OK to proceed with firmware update.  Please ignore Current Version 0.0.0.   Update should complete as normal with no issue.

For the EOS 1Dx

To restart the firmware update please follow the below procedure.

We have found that the EF 40mm 2.8 STM firmware update can fail on a 1D X if the Battery Info is checked right before the firmware update is applied.   In our test cases the Firmware update freezes. The freeze can occur at any percentage of completion.  Other symptoms include a display of 2978% complete and the camera turning off on its own.

To restart the firmware update please follow the below procedure.

1. Remove the battery from the camera.

2.  Reinsert battery, "Firmware update failed. Try updating again." should appear, select OK to proceed with firmware update.  Please ignore Current Version 0.0.0.   Update should complete as normal with no issue.