Hello dear analysts
I used to use overidentifying test by running the following
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ivregress gmm fraud_dummy (CEO_pay_log= local_pay_instrumental industry_pay_instrumental) num_of_CEO_degree_expert num_of_CEO_financial_expertise Fem_indep av_id_age av_id_shareholding board_size ceo_duality board_ind soe big4 roa btm1 eps1 loss_total i.year i.Sic
estat overid
it was working with me well
i got the following result
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  Tests of overidentifying restrictions:
  Sargan (score) chi2(1) =  1.60561  (p = 0.2051)
  Basmann chi2(1)        =   1.5971  (p = 0.2063)
then suddenly when i run same model i get the following finding
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Test of overidentifying restriction:

  Hansen's J chi2(1) = 8.5e-16 (p = 1.0000)
please some explanation
why it became like that.