Hi,
I have a similar problem with the 4Gb sandisk cruzer, more than a "read-only" problem,
the device became "write-protected" , like if i have pushed a small button to enable this feature, but,
the problem is, there are no button ...
so unable to format again, device is write protected regadless the OS ...
i am using a 4 Gb Lexar usb key and it works perfectly.