With credit to bj in his/her response to your post in the worksheet functions
ng, if you remove the ")" following the "IA" it becomes structurally correct
and looks sensible to me. But I suspect this is still not what you intended.

We don't know how your worksheet is layed out and what you are trying to
achieve. You need to specify it. It's not just a simple "fix what's broken"
issue. It's a design flaw and there's more than one way to redesign it.

Note that your first (parent) IF function has only two arguments. This is
still syntactically correct because the third is optional. The formula in
this case will return FALSE by default.

FWIW, pseudo VBA code that translates the syntactically correct part of your
formula follows. Perhaps this logic structure or something along this line
could be used to spell out what you want:

If L2 = "I" Then
If L2 = "R" Then
Return "B"
ElseIf L2 = "F" Then
Return "Ro"
ElseIf L2 = "SCA" Then
Return "Ri"
ElseIf Or(S2 = "IA", N2 = "GBS") Then
Return "GN"
ElseIf AND(L2 = "HC", OR(N2 = "Fi", N2 = "In", N2 = "XC") Then
Return "OM"
<<<<<<< syntactically incorrect beyond here
End IF
End If

Regards,
Greg