URGENT : Need help with Asynchronous Response, I dont recieve it on my end.

In the merchant's "Hosted Paypage Configuration" I have setup Asyncronous Transaction Response. I expect that after the payment, user will be redirected to the page and I will receive a XML response to my server. But i do not receive this XML asynchronous response. I have setup a public post service on my server to receive this response and copied the URL in the Asynch Response URL. ( I have tested this and it works)

Please let me know what wrong? Please help ASAP.