I have been using PayPal for many years with a web store. It is currently osCmax 2.5 (a derivative of osC). For about the last year, I havd had a problem every couple months where a sale shows up on my store, but there was no completed payment through PayPal. When a sale completes, I see a notation on the store's sale page that the sale was completed, with a $ amount, date and time. When it doesn't complete, I get "no data available" in that spot.
Also, it seems that at the same time, I get an email from my store with the subject line "PayPal IPN Invalid Process", and the text :
in the message body. The text from the subject line does not appear anywhere in my store's code, so I'm guessing that IPN Invalid Process must be something sent from PayPal. Does anyone recognize this error message and know what causes it?