Problem after configuring a 1gb Pendrive on Vista Home Basic

hi everybody,
I've got the following problem using a usb 1gb flash device as ReadyBoost.
Once I configured the pen drive for Readyboost to use all the space
available i was able to use it for 30 minutes with no problem whatsoever.
Later, i've disconnected the device using the safely remove option and I've
tried to plug the usb device on another pc with Vista Ultimate.
On the other machine the device manager shows me the pen drive as an UNKNOWN
DEVICE and I can't use the pendrive anymore as readyboost device or mass
storage on any pc.

Is this a regular behavior for a pen drive configured as Readyboost or it
might be a hardware problem?

Any help is appreciated.