SUSE Studio Image Writer (imagewriter) does not work for me (in Tumbleweed).

The GUI opens and I select the image and device and click write.
Then it asks to umount the disk (if it is already mounted).
The partitions are now unmounted.
It now asks me to confirm to overwrite the content of the device, and I click
OK.

Now nothing is happening for maybe 30 seconds.
Then a dialog window appears with the following text:

DBUS error (sdc): Did not receive reply. Possible causes include:
the remote application did not send a reply, the message bus
security policy blocked the reply, the reply timeout expired, or the
network connection was broken.

The dialog only gives me the option to accept this by pressing OK.

Then a new dialog appears with the following text:

Couldn't open /dev/sdc: Resource temporarily unavailable

Again, I have to press OK.