Hi Dimitri,
Did you get to resolve this situation??. I have a FILE -> SAP PO -> Proxy scenario, but in my sender channel also have a module (EdifactConverterModule). I´m facing the same error as yours 'Receiver Determination did not find any receivers at all' and if i choose the 'Not operation-specific' option in the receiver tab, the error is as follows: 'InterfaceDetermination did not yield any actual interface'.
I've been following all the suggestions in this thread but i'm still getting the error.
If you could help me with this issue, i'll be very grateful.
Regards,
Holman Bayona