OJ Board

hi i am unable to understand the reason for PE. it passes all the test cases on the board. i have considered the trailing and leading blanks. i have even tried to remove the blanks within the ISBN's. but still PE
i have already spent 19 submissions for this.
please tell me the reason for PE

I have no idea who you are!!

Please, tell us your id and the submission number you want us to check, or mail us that submission.