Hmm.. this is really strange. I know, that argentina (and maybe some other - like Brazil? But not sure - maybe just argentina one) SBF is un-rootable. But you are saying, that you have rooted it successfully.. So...
Hmm, ok, one last try.
1) install UK GB SBF
(linked in my last post)
2) root it via superoneclick
3) install droid2bootstrap
4) install bootmenu 0.8.6 from my attachment
5) install bootmenu 1.1.0 from my attachment
6) try to install this CM9 http://code.google.com/p/cm9-milesto...estone2-eu.zip
(maybe you will have to wipe data/cache after flashing SBF or after installing CM9, but that's the thing you probably already know...)
... I flashed CM9 that way last time - when my M2 came from warranty service with GB kernel (SBF) in it (so the classic "froyo way" did not worked as last time, before I've sent it to warranty repair)
Good luck and let me know if it helped. I will hope someone else will have better clue if it will not help.