Hi list!
I recently experienced a problem with the TDE Ubuntu 14.04 amd64 iso image: it wasn't accepted as VM cd image in virtualbox.
To exclude a vbox problem, I wrote to their mailing list: one user told me that, an iso image, to be consired a standard image, should have its size dividable by 2048. [1]
I just had a try seeking the image with 2048 as block size and everything is working properly.
Maybe images in the future should be "burned" with that block size?
Thanks! Nick
[1] https://www.virtualbox.org/ticket/14530