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.)

I had this same issue a few days ago, Go back into disk Utility and use the erase option rather than the Partition option. So select the drive you want to get rid off and select erase. Hope this helps