After many days of frustration on trying to get ICS on my Nexus S (i9020a) I found and followed these instructions.
Programming: Tips, Problems, Solutions...: Samsung Nexus S i9020a: Update to ICS 4.0.4 from 2.3.4/2.3.6 (without rooting)
It worked perfectly.
Programming: Tips, Problems, Solutions...: Samsung Nexus S i9020a: Update to ICS 4.0.4 from 2.3.4/2.3.6 (without rooting)
It worked perfectly.