Deleting a partition in Disk Utility fails. (Error: -69879) This is the output in Disk Utility:


  Disk Utility cannot modify this disk because it contains CoreStorage
  physical volumes. Use command line distil instead.
  
  The selected partition won't be changed.


How do I remove the partition?

It's completely empty now and I've cleared it by formatting it but I want to completely remove the partition and merge the free space back into the bigger partition.

I've tried doing this but it doesn't work in Terminal:

diskutil eraseVolume format name device

diskutil eraseVolume HFS+ awer disk1s4


It didn't work: 

Started erase on disk1s4 asdf

Unmounting disk

Error: -69879: Couldn't open disk
Never mind - problem solved.

Turns out that the whole drive's partition table cannot be modified if one partition has encryption on, since CoreStorage is on. (The one that I had on was the encrypt feature for Time Machine.)