Unable to adjust partition of USB drive with Mountain Lion Disk Utility

disk-utilityhard drivepartitionusb

I have a 500 GB USB drive, which I once partitioned into two parts: one encrypted—Mac OS Extended (Journaled, Encrypted), and the other not—Mac OS Extended (Journaled).

Now I want to change the partition layout, and probably add a new partition. However, I was unable to do this in Disk Utility: all options related to partitions are greyed out. See the screen cap for example (clicking on the partitions does not work, either).
screen cap of disk utility
This is pretty weird: not only can't I resize or add partition, I can't make any change to the partition layout, including completely reformatting the disk! Any ideas about this?

Best Answer

You cannot resize a drive that has been encrypted. You will first need to unencrypt the drive, then resize the partitions, then re-encrypt the drive.