Problems with library books

Hi,

I downloaded books from the library and I can open them on the computer with ADE, but when I transfer them on my KOBO ereader I have a message that there is no authorization. My ereader is authorised as is my computer. I deleted the authorisations and made them again. Didn't work. Uninstalled ADE and installed it and tried again and still didn't work. It was keeping the authorisation so I uninstalled it following the steps from the Adobe help deleting files from the regsistry, installed ADE, authorised it, authorised the ereader and again it didn't work.

What to do?