我用的多期DID模型，被解释变量也是虚拟变量这是我的代码：xtlogit Y d_5 d_4 d_3 d_2 d_1 current d1 d2 d3 d4 d5 i.year,fe
回归之后就显示not concave

note: multiple positive outcomes within groups encountered.
note: 592 groups (4,312 obs) omitted because of all positive or
      all negative outcomes.

Iteration 0:   log likelihood = -5585.4512  (not concave)
Iteration 1:   log likelihood =  -5582.908  (not concave)
Iteration 2:   log likelihood = -5582.3778  (not concave)
Iteration 3:   log likelihood =  -5581.094  (not concave)
Iteration 4:   log likelihood = -5581.0126  (not concave)
Iteration 5:   log likelihood = -5581.0066  (not concave)


请问一下，这个问题应该怎么解决？