[Limdep Nlogit List] GMXL in WTP space (optimization)

[MARÍA DEL PILAR ESPINOSA GODED]

Hello, i am trying to run a GMXL model in the WTP space and i get the following message
Line search at iteration  1 does not improve the function
Exiting optimization
With <   4 iterations, this may not be a good solution to
the optimization. The log-likelihood is flat.  Try refit-
ting with ;Output=3 and examining the derivatives."

Below the model. (when i run the model without fixing the payment atribute to 1 - i do not get the message). Thanks!!!!!

|-> GMXLOGIT; Lhs = Choice_L ; Choices=1,2;
    ;fcn=AUSED(N|#0001000),AUSEA(N|#1000000),  ANAT(N|#0001111), AFAFA(N|#0011000),AFAFO(N|#0001000),AINF(N|#0101010)
    ,AWOD(N|#0010000), AWOA(N|#0010000), ABUFA (N|#0000101),ABUFO(*N|#0000000)
    ;rpl=region1, etud_b, female, ageC,seniorz0, seniorz1, seniorz2
    ; model: U(1,2) = AUSED *Cuse_d_A + AUSEA*Cuse_a_A +  ANAT*Cnatu_A + AFAFA *Cfa_fa_A + AFAFO*Cfa_fo_A + AINF*Cinfo_A + AWOD* Cwo_d_A + AWOA* Cwo_a_A +ABUFA* Cbu_fa_A+ ABUFO* Cbu_fo_A
    ;  Pds = 9  ; Draws=75;parameters; maxit=400$