The upgrade of the cluster software could not proceed because there is an I/O group in the cluster that contains only one node. The software upgrade requires that each node in an I/O group be shut down and restarted. If there is only one node in an I/O group, I/O operations could be lost if I/O operations are not stopped before beginning the software upgrade.
Either upgrade the cluster using the -force option or specify a different node, and resubmit the command.