That message is from Aldiko, not from ADE. I believe it's telling you that
there's an error in the format of the ebook that won't let Aldiko go any
For reference if others are seeing curl return codes in this error message. Curl return codes can be found at: libcurl - Error Codes
In this case
The URL you passed to libcurl used a protocol that this libcurl does not support. The support might be a compile-time option that you didn't use, it can be a misspelled protocol string or just a protocol libcurl has no code for.
I am sorry, but I disagree with that message from Aldiko. It is not the format of the ebook. Let me tell you this: I had bought some ebooks DRM protected and uploaded on Dropbox, and anytime I needed to open them, I just tapped on them and everything was ok. NOW everytime I try to download these same files, or ebook files from TWO different online stores (one located in Spain, and the other in Australia!!) where they are kept in "my eBokk library", I can see the "downloading successfuly" message, and then that terrible message that doesn't let me read them anymore! And, yes, strangely, the same problem happens with PocketBook, in my TWO tablets. So, clearly it is ADE.