What is test 8?
I tested my program for 9<=n<=200 brute force and my answers is right.
For 1<=n<=8 output is:
i : NO when i<=n-1
n: aaaaaaaa (n times)

This is not true for n = 8. The correct answer is:
1 : NO
2 : NO
3 : NO
4 : NO
5 : NO
6 : NO
7 : aababbaa
8 : aaaaaaaa

Thanks! I got AC! My error: I found solution for n<=8 by hand.