Have an 1100 AP with ACU 6.1 client, goal is to upgrade to the ssc 4.2.1 client, but the upgrade needs to be silent. Here is how we got to work.
With 6.1 installed need to install SSC 4.2.1 on the box, then install ACU 6.6 (build a silent install with ACAT dat file) reboot will keep you networked on open and now should allow for WPA authentication. Last step is silent uninstall of the ACU 6.6, which is
(iwsetup -uninst -silent)
SSC 4.2.1 does not have an option for firmware upgrades to the card. ACU 6.6 has that option, also you can have ACU 6.6 and SSC 4.2.1 running at the same time, however ACU 6.6 will control the radio over ssc by default, in order to have ssc 4.2.1 active with ACU 6.6 need to right click on ACU client in the notification far right toolbar, then select profile check mark Use other Configuration Application). This way you can use the XML profile features as well as still be able to do firmware upgrades to the card.