求助：我在stata里面做回归，是混合截面数据，要用logit命令，下面是我的命令：
xtset year
xtlogit ICAO RAcindep RAcexpert Acmeet Acsize State Size LEV ROA GROW NS AO if State==1
我想给他分类按State==1和State==0分别进行回归。可是当我输入这个命令后，我的result里面出现这个界面：tion 3701: log likelihood =  2.217e-16  (not concave)
Iteration 3702: log likelihood =  2.217e-16  (not concave)
Iteration 3703: log likelihood =  2.217e-16  (not concave)
Iteration 3704: log likelihood =  2.217e-16  (not concave)
Iteration 3705: log likelihood =  2.217e-16  (not concave)
Iteration 3706: log likelihood =  2.217e-16  (not concave)
Iteration 3707: log likelihood =  2.217e-16  (not concave)
Iteration 3708: log likelihood =  2.217e-16  (not concave)
Iteration 3709: log likelihood =  2.217e-16  (not concave)
Iteration 3710: log likelihood =  2.217e-16  (not concave)
Iteration 3711: log likelihood =  2.217e-16  (not concave)
Iteration 3712: log likelihood =  2.217e-16  (not concave)
Iteration 3713: log likelihood =  2.217e-16  (not concave)
Iteration 3714: log likelihood =  2.217e-16  (not concave)
Iteration 3715: log likelihood =  2.217e-16  (not concave)
Iteration 3716: log likelihood =  2.217e-16  (not concave)
Iteration 3717: log likelihood =  2.217e-16  (not concave)
Iteration 3718: log likelihood =  2.217e-16  (not concave)
Iteration 3719: log likelihood =  2.217e-16  (not concave)
Iteration 3720: log likelihood =  2.217e-16  (not concave)
Iteration 3721: log likelihood =  2.217e-16  (not concave)
Iteration 3722: log likelihood =  2.217e-16  (not concave)
Iteration 3723: log likelihood =  2.217e-16  (not concave)
Iteration 3724: log likelihood =  2.217e-16  (not concave)
拜托大家我该怎么办？