If it does not have a physical switch and is not worn out so it will only read now, and if you are using Windows 7 do this, a quick diskpart correction:
Open the command prompt box with right click and run as administrator
Type each of these commands one at a time in this order:
select volume n (where n = the problem volume, i.e the write protected one)
attributes disk clear readonly
attributes volume clear readonly
After each of the last two you should get a response that it was successful.
Reboot after you remove the device and then reattach.