Tente usar cihper d:\ /e
.
cipher /?
:
Displays or alters the encryption of directories [files] on NTFS partitions.
/e
:
Encrypts the specified files or directories. Directories will be marked so that files added afterward will be encrypted. The encrypted file could become decrypted when it is modified if the parent directory is not encrypted. It is recommended that you encrypt the file and the parent directory.