USB Stick keeps changing back to read only

Hi

I'm running Knoppix 5.1 Live CD with an 8GB Everex USB stick on my Thinkpad T43.
All of the time the stick can be mounted and switched to read/write, no problem.

The stick has a short simple name USB8GB.

BUT! Some of the time the USB stick flips back to read only (can take 5-30 minutes but never longer).

I don't see the same issue on my home PC with OpenSuse or on Windows XP, so the hardware is OK...

Any ideas how to stop this happening?

Thanks

Gryff