dfu-util: Cannot claim interface 0

[janj]

I'm trying to update my firmware on my Pycom Expansion board V3.0.
I'm running Fedora 28.
When following instructions acording to https://docs.pycom.io/pytrackpysense/installation/firmware
//
To enter update mode follow these steps:
Unplug the device
Press the button and keep it held (on the Expansion Board the S1 button)
Plug in the USB cable to the host computer and wait 1 second before releasing the button
After this you will have approximately 7 seconds to run the DFU-util tool
macOS and Linux:
$ dfu-util -D pytrack_0.0.8.dfu
You might need to run dfu-util as sudo. In that case, you will need to enter your password.
//

own output:

sudo dfu-util -D expansion3_0.0.9.dfu
dfu-util 0.9

Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2016 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to http://sourceforge.net/p/dfu-util/tickets/

Match vendor ID from file: 04d8
Match product ID from file: ef99
Opening DFU capable USB device...
ID 04d8:ef99
Run-time device DFU version 0100
Claiming USB DFU Runtime Interface...
dfu-util: Cannot claim interface 0

Google didn't help me so far.

[janj]

Solved. My mistake. I just connected to the expansion board, without the WiPy module on top of it. Then it had the error.
With the WiPy module connected to the Expansion board, and following the instructions, the firmware update went fine.