Ice-cream-sandwich was installed on my Galaxy S II but face recognition or PIN security works only first time but not subsequent times after sleep reopening?

You could try a factory reset, probably wise after going from Android 2 to 4.

Do factory reset. If doesn't work then http://goo.gl/YysjW

Doing a wipe data/factory reset will clear out any remnants of the previous version of the android OS, if not done you can get conflicts between the old and new Versions.

Face recognigtion should work fine once set up.