If you are 100% sure that you have a good, non corrupted image, then my guess would be: I've noticed that Ubuntu has some bug with a few sATA connectors. I've got the official Ubuntu disks shipped home and Ubuntu installed on every machine with an ordinary IDE disk, but never on sATA.
If you have a ATA disk, you might have the same problem I had. I've managed to install it afterward, by "rebooting - try again". After a couple of times, Ubuntu installer did not spit the above error message and installed fine.
I did it multiple times and it is indeed a bug on the installer. If you are patient enough, keep trying.
About patience, according to the rules, you are not supposed to bump a thread in less the 24 hours: