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

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?
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.