I have been experiencing problems uploading books after many months without issues. The Kobo Customer Service went through different steps with me including updating my Adobe Digital Edition and removing the e-reader authorization and reactivating it. Still not working.
They indicated that it might be an issue related to my Adobe ID. I tried getting answer from the Adobe support team, but they referred me to the Forum.
Anything you can do to help? It seems that my Sony E-reader PRS-T1 doesn't recognise my ID anymore.