It's a year later, but I've just encountered this issue myself and tried the CLI options. For the sake of accuracy to the above 'answer', I'm adding my conclusion here.
aborzenkov is correct. You can enable the licensed_feature option, and it will resolve your iSCSI issue without having to resort to System Manager.
> options license
> options licensed_feature.iscsi.enable on
Run 'iscsi start' to start the iSCSI service.
Also run 'lun setup' if necessary to configure LUNs.
> iscsi start
iSCSI service started