An attempt to establish, suspend, or terminate a PPRC pair resulted in communication error between the primary and secondary control units. Possible causes for CKD are:

• The secondary device is busy.
• The secondary device is reserved.
• The secondary is participating in a concurrent copy session or an XRC session that is not suspended.

Possible causes for FB are:

• The LUN is long busy.
• The LUN is not installed.
• The LUN is waiting for a Start Unit command, with Format Failed status.
• The LUN is active on another interface.
• The LUN is in a hardware failure state.
• The LUN is performing a Write Same or Format Unit.
• The secondary performed a Release Space (initiated by an establish PPRC pair or Establish FlashCopy® pair) and the release space of the secondary/target volume is not complete.