Challenging Math Problem

A couple days ago, the following math problem was published on Singapore TV. Although the problem was designed for ten year old students, it has stumped adults around the world. Do you think you can solve this word puzzle?

Albert and Bernard just become friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates.

May 15, May 16, May 19, June 17, June 18, July 14, July 16, August 14, August 15, August 17

Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively. 

Albert: I don't know when Cheryl's birthday is, but I know that Bernard does not know too.
Bernard: At first I don't know when Cheryl's birthday is, but I know now.
Albert: Then I also know when Cheryl's birthday is. 

So when is Cheryl's birthday?

I spent at least ten minutes trying to dissect the grammatical errors thinking that Albert and Bernard were passing each other clues. Only after reading the solution did I realize that the grammar was probably the result of translation and was not deliberate...

Do you give up yet? You can find a step by step solution here.