I have not seen the mistake so far, what is it?
Is it possible that the Activity-Main is in pause and the system tries to execute the function "GetOwnedProducts"?
Private Sub billmanager_BillingSupported (Supported As Boolean, Message As String)
'Log(Supported & ", " & Message)
'Log("Subscriptions supported: " & billmanager.SubscriptionsSupported)
IsBillingSupported = Supported
If Supported Then
CallSubDelayed (Main, "GetOwnedProducts")
End If
End Sub
This error means that there is already another operation happening. This can happen if you call GetOwnedProducts twice or maybe you called RequestPayment.
Note that you can catch this error with a Try / Catch block.