Curious Problem: MacBook Pro not recognize Usb External H. Disk (SimpleTech/Pininfarina 250g. Fat32).

Hi all

I have a new Mac Book Pro Intel 7i and an external USB drive (SimpleTech-Pininfarina 250g. Fat32). The Usb disk by connecting power-light comes on but the mac does not recognize, after a couple of hours connect to mac, if I connect and reconnect the USB Disk appears on the desktop and I can be accessed onnormally.

The Usb Disk operate normally on other computers, mac and pc. No same to my model.

Which could be the problem and how can fix it?

Thanks for your time and answers!