I have just had that problem, I raised a ticket, no 4146, its closed now. Mine was intermitant, I reverted back to a slightly older version of calibre 6.23, and reformatted my reader which wiped it clean. I had a really full harddrive and (touch wood) its seems to be okay now, and much faster with not so much on it.
I didn't get 'Trying to Open Device - Failed' though so can only sugest you raise a bug ticket
|