Shotwell cannot mount device Error 53

Solution 1:

This is this bug: https://bugs.launchpad.net/ubuntu/+source/shotwell/+bug/1400470

As a workaround for now, try unmouting the camera in Nautilus and starting Shotwell.

Solution 2:

One way I got round it (connecting a Cannon EOS 700 to Linux Kubuntu with Shotwell) was simply to use another of my PC's USB connectors. Suddenly one of the other USB connectors around the back of the PC worked. Don't ask me why. I hope this helps others.

Solution 3:

This issue is caused by Nautilus mounting the camera automatically and therefore locking the device.

One workaround that did work very well for me was to disable the automounting in Nautilus as described in detail here: How to disable automount in nautilus's preferences

When you disable the automounting, you can still mount the external devices manually, if needed, by clicking on them in Nautilus.