Paypal customers not receiving confirmation e-mail

[danbug]

I have 2 stores that I upgraded from 1.37 to 1.39d.
One of the stores works fine, but the other one won't send a confirmation e-mail with the download link to the customer for books they buy. What's more, their purchases don't appear in the order list or in their customer history.
I've spent days going through IPN setting and trying to determine what the difference is.
Does anyone have a clue?

TIA, danbug

[DrByte]

When orders placed with the "PayPal Website Payments Standard/IPN" module don't show up in your store, that's a direct result of a problem occurring when PayPal's server cannot talk to *your* server to tell it about the new order.

Recommended course of action: Click "Remove" on "Website Payments Standard", and click "Install" on "PayPal Express Checkout".
Express Checkout is much more reliable, as it doesn't depend on PayPal's archaic IPN architecture to get orders into your store.