Not a Sandisk by any chance? They have firmware protection build in which kicks in if something bad is happening to drive so it makes the drive RO, so no corruption happens to the data (unknown what actually triggers the process) Nice if you look at it one way, totally nuisance looking the other way Whatever, once RO is imposed the drive it just that & will never again be writable. With Sandisk manufacturer will replace the drive if within 5 years of warranty period, but one has to post it back to Czech Republic (hardly worth for ie 4 Gb stick)