That command worked for me, at AOS 6.4.2.1-FIPS. Not sure if maybe it's just not present in 6.4.1.0. If you run a "no firewall ?", what is the output?
(Aruba7010) (config) #no firewall enable-stateful-icmp
(Aruba7010) (config) #show image ver
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Partition : 0:1 (/dev/usb/flash2) **Default boot**
Software Version : ArubaOS 6.4.2.1-FIPS (Digitally Signed - Production Build)
Build number : 46041
Label : 46041
Built on : Thu Sep 18 02:50:20 PDT 2014