You cannot start or prepare a map while the target of the map is the source VDisk of another FlashCopy mapping that is being restored.
Ensure that the target VDisk in the map that you are attempting to start or prepare is not the source VDisk of another FlashCopy mapping that is being restored when you submit the task. You could stop the associated map that is being restored, or you could wait for the map that is being restored to reach the Idle_or_Copied state.