05A

Explanation
Alternate CPU recovery (ACR) attempted to remove the last standard CP. There must be at least one
standard CP online in order for the system to run.

System action
The system issues message IEA856W and enters a non-restartable wait state.

Operator response
Notify the system programmer.

System programmer response
The system has lost access to the last standard CP and can not run in this mode. If the CP was
lost due to hardware failure, it will require the LPAR to be reconfigured to have at least one
usable standard CP. If the CP was taken offline due to a software error, then reIPL the system.

Source
Alternate CPU recovery (ACR)