I think i found the problem, producing the error. In the documentation i red, that "the values in the target vector (in my case y_true) have to be: 0 <= y_pred[i] <= C-1.
In my case C = 1, so all the values y_pred[j] = 1 are out of range.
Since I can’t change my input vector (y_pred), I don’t know, how to use the CrossEntropy Loss for this binary problem properly.
Can anybody help me please?