setup.exe used with both /acu and /ncpf: switches returns an error

Attempting to run an NCL Upgrade from a previous client fails when using the following line:

setup.exe /acu /ncpf:settings.txt

An error is returned:

The Novell Client Installation is already running on this Windows machine. 
Please complete and close the existing Novell Client Installation program
before attempting to run SETUP.EXE again.

Workaround:

Simply run the acu.exe and specify any particular settings in the unattend.txt