Sandisk Cruzer Micro flash drives - problem

Has anyone else had problems with these? Out of four 256MB versions that
I purchased for rotating backups, two have failed in the same way - each
worked for a while, then gave problems loading data, then could not be
recognised by the system at all.
I have several other devices, including the remaining two Sandisk drives
and the 64MB flash drives that I used previously, working fine. These
also work on different PCs, but the failed two don't work on any PC that
I have tried.
On searching the net (yes, I know I should have done this first, but I
assumed Sandisk were a good company) several similar instances appeared;
it seems to be a component failure. I haven't had any response from
Sandisk itself, but I'm told they aren't very helpful anyway.

Just in case: Does anyone know of a software fix to this problem? Or
perhaps a method of either retrieving or wiping the data?

And of course: If you are using these drives, DON'T rely on them as your
only backup of anything critical! (That's why I have several flash
drives used in rotation, and burn a CD weekly.)

Dave