Hello,
You shoud use PSID revert tool from disk manufacturer (for example SANdisk) that will wipe out drive, but you will be able to use it - now it is locked and you can not use it, right?
It seems that there is an issue with SEE when you decrypt drive from SEE client, it does not update drive status and if you use drive tool to check drive/disk state you will see that it is still encrypted. We have case opened for very similar issue (Case # 11774851) and still no solution.
If you do not care for data on that drive, easy way is to use PSID revert tool and wipe/reset it to be able to use it (you will need to reinstall everything after that and you will lose ALL data on it!).
Regards,