Bitlocker: Cannot auto-unlock USB drive. "The drive cannot be encrypted..."

Question

My system drive (C:) and external USB drive (D:) are both encrypted with Bitlocker.

I can unlock the D: drive with the password. However I cannot get it to auto-unlock. Checking the box doesn't do anything. At next login it still requires the password to unlock again.

If I go to "Manage Bitlocker" for the drive and click on "Turn on auto-unlock", I get the following error...

The error doesn't seem to make any sense, as the drive is already encrypted.

I don't know what it means about the system boot information, as this is a data drive which has never been used to boot an OS.

I have previously been able to get this drive to auto-unlock, but have since re-installed Windows 10, to get the SSD hardware encryption working.

Just a bit more information about the system, if it's helps.

The system drive is a Samsung 850 Pro SSD, with "Encrypted Drive" enabled through Samsung Magician.

The external USB drive is a 3TB Seagate.

The system doesn't have a TPM, so I'm using a boot password to unlock the system drive.

I have considered turning Bitlocker off and on again for the external drive, but I would really rather avoid that if possible, as it will take an extremely long time, and may not do anything anyway.

Answer 1

If your disk is NOT a boot disk containing your Windows installation (system drive), the only way I found to fix it to be able to auto-unlock the drive is to temporarily move/backup the files contained on this disk onto an other disk, I deleted the disk partitions for this HDD to remove the boot details it could contain and recreated a single NTFS partition on it. After this, I formatted the disk and turned ON Bitlocker to encrypt it (really fast if empty) and I completed by moving back the files/backup onto this disk. Once done, auto-unlock should be working on this disk. This process can take a while to copy all the files back and forth, but at least it's now working like it should.