A volume cannot simultaneously be both the source of a FlashCopy mapping and the target of a FlashCopy mapping. A source volume was specified that is currently defined as the target of a FlashCopy mapping.
You have two options. One option is to specify a different source volume and resubmit the command. The other option is to delete the existing FlashCopy mapping that defines the source volume that was specified as the target volume, and resubmit the command.