Prime31 storekit "product already purchased"

HI

I use Prime31 storekit in my game. Everything is fine. But sometime, when i buy one product for the second time in one session, i have one error message that say to me: (the message is in french, but in english it's something like that) "you've already purchased this product, but it wasn't donwloaded, click OK to download it now" And in Xcode debug area i have this message from storekit: "StoreKit: cancelled transaction: Connexion Itunes store impossible"

Anyone know this issue, and how to fix it?

thanks

Baptiste