|You best bet is to contact Western Digital and see if they can help you. As it was they that wrote the software is is they that that will have the best idea of how to decrypt the data. They may have a back door password that might work. |
Cracking 256 bit encryption is no trivial task. It is usually only the CIA and similar organisations that have the resources to do such a thing.
However, you will almost certainly be asked by WD to prove that you actually own the disk and the data therein is yours. They are not going to decrypt a hard disk just because someone asks them to and it will cost you. They are not going to do this for free.