First, make sure that the pen drive [I'm assuming this is a USB drive] doesn't have a "write protection" switch as I believe some of them do. Make sure it's in the "unlock" position. If that's in the clear, plug it in and go into "My Computer," "Right Click" on the drive and go to properties. There should be a "Read Only" switch in there that you can toggle on/off. Make sure it is unchecked. This will disable write protection in any device or folder.

