"Erase process has failed. Click Done to continue."
I want to erase a partitioned (and fairly new) external HD, using Disk Utility, so I can repartition it. I've clicked "Show all devices", selected the HD (as opposed to the individual partitions), gone with the default format (Mac OS Extended (Journaled) and scheme (GUID Partition MAP), and clicked Erase. DU tries erasing, then tells me "Erase process has failed. Click Done to continue."
How do I sort this?
iMac Line (2012 and Later)