I just had the exact same problem when trying to install with an encrypted LVM. I saw the "Failed to determine the codename for the release" error, and when I checked the validity of the image I also got that same error.
I just had the exact same problem when trying to install with an encrypted LVM. I saw the "Failed to determine the codename for the release" error, and when I checked the validity of the image I also got that same error.