@julian exactly that was the problem, thanks for the hint!
for others who face maybe similiar issues:
The following format worked for me (.csv format):
Is there any plugin can assign "Score" when user post? it more like a reward system, when user submit a post with questions that he/she usually will also assign a "Score" to the post, so, any one who answered the question will gain the "Score". any Plugin or configuration can do that?