Paypal isn't sending back info

I’m trying to figure out why, when I do a test purchase on my web site,
that the purchase completes at Paypal, but the purchase info is not being sent back to the site. It worked successfully, but for some reason now it is not. Any thoughts/suggestions would be apprecaited.

When I was debugging IPNs, the very first line of the script that received the IPN wrote to a log file. That way I could tell at least if it was being called.

yes IPN

Are you talking about IPNs (instant payment notifications)?