Access Denied on Paypal IPN verification

I started getting errors during IPN validation since Sept 2014 WITHOUT any CODE CHANGES in my e-shop
I receive payments but there isn't any orders registered.

I contacted Paypal thechnical support and they told me that I need to include my MerchantID as User-Agent in the HTTP Header.

Could you please help me - where in the script I have to add this option?

Thank you

I don't know about Paypal's advice, but switching to Paypal Express should solve your problem. There's no reason I'm aware of to use Paypal Standard any more.

Thank you

I've tried ExpressCheckout but I have a lot of troubles with this payment method.
My site currency is BGN (1EUR = 2BGN), when the customer goes to paypal web site to make a payment paypal shows the correct price in EUR but after payment is completed the real amount the customer is charged is the value in BGN. In this way if the order is 10 BGN the customer pays 10EUR instead of 5EUR.

Also if a customer set a shipping addres in my site the paypal replaced it with the shipping address in his/her paypal account. This causes problems because we deliver flowers and usualy the shipping address of the order is different from teh shipping addres in the customer paypal account.