oki
This is a simplified code but I have the same problem :
In A1 put "poui"
in F1 put "poui", in F2 put "grr"
in G1 put 1 in G2 put 2
the code:
public sub maisquestcequisepasse()

range("B1").select
activecell.formulaR1C1 ="=vlookup(RC[-1],F:G,2,false)

end sub

I just think I may have find it: VBA does not understand F:G........
GRRR I am stupid !!!!!!!!!!!!!!!!!!!!
Thanks for help Patrick and have a nice year
Benjamin