Problem with ml model with panel data and misclassification error

[Brama Dial]

Dear all,

I'm trying to implement Hausman et al (1998) misclassification error for binary choice model with panel data. ml check give me an error : Two different coefficient vectors resulted in equal log likelihood values r(9). I don't know how I can fix it. Do you have any suggestions? Many thanks and best regards,

program drop _all
program define mrpr
    version 16.1
    args   todo  b lnfj  
    tempvar mylnf xb alpha0 alpha1 last 

    mleval `xb'=`b', eq(1)
    mleval `alpha0'=`b', eq(2) scalar
    mleval `alpha1'=`b', eq(3) scalar
    scalar `alpha0'=invlogit(`alpha0')/2
    scalar `alpha1'=invlogit(`alpha1')/2

    local by $My_panel
   sort `by'
   by `by'    : gen `last'=(_n==_N)

   gen double `mylnf'=0
   replace `mylnf'= $ML_y1 *ln(`alpha0'+(1-`alpha0'-`alpha1')*normal(`xb')) +(1-$ML_y1 )*ln((1-`alpha0')-(1-`alpha0'-`alpha1')*normal(`xb')) if  `last'==1

    mlsum `lnfj'=`mylnf'

     *if (`todo'==0 |`lnfj'>=.)  exit
end


global My_panel personid
ml model d0 mrpr (xb: yvar= `covariates' ) /alpha0 /alpha 


.ml check

Test 1:  Calling mrpr to check if it computes log likelihood and
         does not alter coefficient vector...
         Passed.

Test 2:  Calling mrpr again to check if the same log likelihood value is
         returned...
         Passed.

Test 3:  Calling mrpr to check if 1st derivatives are computed...
         test not relevant for type d0 evaluators.

Test 4:  Calling mrpr again to check if the same 1st derivatives are
         returned...
         test not relevant for type d0 evaluators.

Test 5:  Calling mrpr to check if 2nd derivatives are computed...
         test not relevant for type d0 evaluators.

Test 6:  Calling mrpr again to check if the same 2nd derivatives are
         returned...
         test not relevant for type d0 evaluators.

------------------------------------------------------------------------------
Searching for alternate values for the coefficient vector to verify that mrpr
returns different results when fed a different coefficient vector:

Searching...
initial:       log likelihood =     -<inf>  (could not be evaluated)
searching for feasible values +

feasible:      log likelihood = -39456.325
improving initial values ++++......
improve:       log likelihood = -37414.699

continuing with tests...
------------------------------------------------------------------------------

Test 7:  Calling mrpr to check log likelihood at the new values...
         FAILED.
         Two different coefficient vectors resulted in equal log likelihood
         values of -37414.699.
         This does not prove there is a problem, but it suggests it.

two coefficient vectors:
           xb:        xb:        xb:        xb:        xb:        xb:         /:         /:
          did       sexe    mdefipc   agegroup  educgroup      _cons  alpha0  alpha1
r1          0          0          0          0          0   67.07219   69.31779   35.76148
r2          0          0          0          0          0          0          0          0
r(9);