[arch-general] automount failure usb storage

[message]

Readers,

USB storage media used to appear automatically on the xfce desktop, but 
not now.

From dmesg | tail:

uas: probe of 3-1:1.0 failed with error -12

Automount has seemingly failed today. The udev wiki 
(https://wiki.archlinux.org/index.php/Udev) doesn't make sense to a weak 
novice like me. Other advice please?