I've twice downloaded ubuntu-12.04.4-server-amd64.iso from the Ubuntu site, and when I'm somewhere through the installation, I get the message in the screenshot below. How do I get past this? The image cannot be corrupted twice. What am I doing wrong? Or are the iso images themselves corrupt?
I'm doing all this on a Dell Laptop with 4GB RAM running Windows 7 Home Premium 64. I'm using Oracle VirtualBox.
When I run check cd-rom, I get this: