Different models or generations of nodes might have different numbers of Ethernet ports. If the system is created with multiple nodes that have different supported node models, the source port ID that you specify (either by using the management GUI or by using the detectiscsistorageportcandidate command) cannot be greater than the highest port ID on any node that is part of the system or specified I/O group.
Check the number of Ethernet node ports present on each node by using the management GUI or the lsportip command. Run discovery again, and this time specify a port ID within the available range.