What PPF law says -
If a subscriber does not subscribe Rs. 100/- in the first year, subscriptions paid by him will be refunded to him without interest, simply because the account is not considered as validly open. But if the subscriber after paying Rs. 100/- in the first year, defaults on the minimum subscription in the following year, he can continue with his PPF account only after paying the Accounts Office the prescribed default fee along with the arrears in the subscription.
In your case you have deposited Rs. 500 in the first year, so your account is valid. Second point that in year 2010, you have deposited Rs. 100 (less 400 than the min subscription of Rs. 500), so its fine for this year but from the year when you wants to start investing again in PPF account, you have to pay default fee and the arrears in the subscription.