USB not recognized after installing OS X Snow Leopard on it
"Cannot write to last block of device" is usually a connectivity error - it often crops up on HDs &amp; SSDs with a bad cable.

For it to happen on a USB stick, then I'd say either the contacts are dirty or the device is dead [or dying].

You could try cleaning up the contacts with a bit of contact cleaner, then push/pulling the stick a dozen times in &amp; out of a [non-powered] USB socket.

If that gains nothing, then I'm reasonably certain that if it's failing on three different machines, then it's had it.