App crash on inapp billing

Hello,
i maked a test buy over testflight and always the app crash...

the complete code:

Code:

  Sub store_PurchaseCompleted (Success As Boolean, Product As Purchase)   
If Success Then       
Dim no As NativeObject = Product
Dim b() As Byte = no.NSDataToArray(no.GetField("transactionReceipt"))

Dim bc As ByteConverter

        acc.setPro(email,md5Passwort,Success,bc.StringFromBytes(b, "UTF8"),secID)
End If
End Sub  

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