FYI, it seems the link changed, but the solution still works! Here is the update to the link Sintek posted (thanks!)
Windows Write Protection T3CHWORKS -
And here is an exerpt of it, in case it changes again:
Recap
Start > Run "cmd"
type--> diskpart
type--> list volume
type--> select volume #
type--> attributes disk clear readonly
Thanks to the owner of T3CHWORKS!
Thx!!! this thing help me to solved my unwriteable external HDD problem

for those who failed, keep trying and try pull out the external disk and try to other usb ports... it works for me at least

My Computer
- OS
- Windows 7