In regards to Chip Piller's comment #17, I can confirm I was experiencing the same issue with a Toshiba Portege R835-P50.
I was trying to install Linux Mint 11 from a USB created with UNetbootin. I received the message when the USB stick was in the USB 3.0 port. Swapping it over to the 2.0 port allowed it to work fine.
In regards to Chip Piller's comment #17, I can confirm I was experiencing the same issue with a Toshiba Portege R835-P50.
I was trying to install Linux Mint 11 from a USB created with UNetbootin. I received the message when the USB stick was in the USB 3.0 port. Swapping it over to the 2.0 port allowed it to work fine.