I remove all the partitions, create a new one, format the drive and then I regain its use.
You didn't tell if you needed to save files.
I bought this hard drive on Boxing Day http://tinyurl.com/9zv8ux and I have used True Crypt to make two containers on the drive. One 200GB and one 265GB.
I moved some stuff over from my notebook to free up space and everything went fine. The next day however, I tried to write to it and it said it was write protected. I have no idea how that happened.
I've looked around for a solution and nothing has helped.
I'm running Vista Business 32 bit if that helps any, thanks.