Shopping cart becoming empty

Hi,

I have a site based on nopCommerce, when a client buys a product and moves forward to login or registering to our site. When client login that time the cart becomes empty. But if the client was already logged in and then purchases, then cart won't become empty. We got this problem from 2-3 days, before it was working fine.

Thanks in advance for any kind of help.

You might need a machine key.  Google the forums for more info.