If you are using a Dataflow and you are getting that error I would turn in a ticket to Microsoft to confirm that on their side they have the right version of npgsql installed since I believe that it is their install and not yours that is used in a Dataflow. Please let us know the result.
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Thanks for the response. The dataflow executes trough the gateway and not from the Microsoft side. The version of npgsql is the correct version. We have a ticket opened with MS, so hopefully we can get it resolved at some point.