My pendrive shows write protected and use another... (by 3 users)

First try to see is there any lock in your usb pen drive and see if its not locking the pen drive, because some pen drives comes with that option to protect usb .it looks like slide switch .for one end it will lock the media and when you switch to other side you have the full access
but if that's not the reason it might be the problem with registry

Use the Registry Hack to Disable Writing to USB Drives
Here is the link .just download the zip folder and after opening the folder you will find a file just double click on it..

http://www.howtogeek.com/wp-content/uploads/DisableUSBWrite.zip
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If you take the hold switch/button/function off the portable drive/watch/whatever and reconnect the leads it should now work. Good luck!
himani kapoor