Paul - this is not an error, rather it shows that the product is working as intended:
A Windows service called "Interactive Services Detection" notifies the user that a program window has been opened in an isolated session when the NPrinting engine service opens a QlikView Desktop instance to generate a report. This is not an error message. This message does not have any effect and it is just informing you that there is an interactive service running. You can safely ignore this or stop and disable this service using services.msc but this will stop all ISD messages not just the ones triggered by NPrinting. I would simply ignore it rather than disable it.