Hey Gernot,
Welcome to the community of the desperate! I gave up waiting for any help from the developers. It seems to me like the support for usb keyboard was removed from the device software some time after that successful youtube video (which was a big reason why I bought the device!). Maybe they just don't want to own it; boxtor is known to be quick in his replies, but not this time, apparently.
I am rather disappointed with my reader at this stage. First, a good portion of apps I am using (including OneNote app and Firefox) now require Android 4.1 and higher; if I spend a day and force them to install, they don't work properly. Second, even after all the updates, the screen is too imprecise even for highlighting, not to mention any text imputting with the software keyboard - and I need to comment a lot on what I'm reading. I have not found any bluetooth keyboard case that would fit; I do have a usb one that does fit, so I was rather hoping that the usb issue would be resolved. Apparently, not in this lifetime
