[Limdep Nlogit List] Fixed effects model: Error 682

[Pavlos C. Symeou]

Dear Limdep-listers,

I am trying to estimate a Fixed Effects Frontier Model using the 
following commands.

Frontier    ; Lhs = ly1; Rhs = one, xs;     Rh2 = one, zs;     Model=T $
Frontier    ; Lhs = ly1; Rhs = one, xs;     Rh2 = one, zs;     Model=T
                  ; FEM        ; Pds = ni $

Running it though gives me the following error:

Error   682: Did not find matching previous nonpanel FRONTIER model.

Can you please advise me on this?

Yours,

Pavlos