This occurred again today.
Aborted from 14.10 (fully updated) after 'prompt to upgrade to vivid', which looked like it would take forever.
Restarted Notebook, to install 15.04 using USB of 'Ubuntu 15.04 Desktop (64-bit)' (release).
When prompted with 'non-UEFI' mode warning, I choose 'back' and removed ALL existing partitions, then powered off.
Then re-ran, with NO repeat of issue.
This occurred again today.
Aborted from 14.10 (fully updated) after 'prompt to upgrade to vivid', which looked like it would take forever.
Restarted Notebook, to install 15.04 using USB of 'Ubuntu 15.04 Desktop (64-bit)' (release).
When prompted with 'non-UEFI' mode warning, I choose 'back' and removed ALL existing partitions, then powered off.
Then re-ran, with NO repeat of issue.