apple In App Purchase always response 20112

Hi，I am facing the 21002 issue.Have you went through it? If you have resolved it, please dive me a hand.
Below is my code,and I Have tested in sand box environment. NSURL receiptURL = [[NSBundle mainBundle] appStoreReceiptURL]; if (![[NSFileManager defaultManager] fileExistsAtPath:[receiptURL path]]) { SKReceiptRefreshRequest receiptRefreshRequest = [[SKReceiptRefreshRequest alloc] initWithReceiptProperties:nil]; receiptRefreshRequest.delegate = self; [receiptRefreshRequest start]; return; } NSData data = [NSData dataWithContentsOfURL:receiptURL]; / receipt_data/ NSString *receipt_data = [data base64EncodedStringWithOptions:0]; After I test the purchase procedure, use the above receipt-data to verify on the server https://sandbox.itunes.apple.com/verifyReceipt,which always response 21002.I have no idea to deal with it.Thanks.