I had this same issue (Netscaler 10.1). Turns out I needed to turn on Appflow for the Netscaler Gateway virtual server. In 'Configuration > NetScaler Gateway > Virtual Servers', click a Virtual Server and open it. Along the top of the window are some check boxes, one of which is 'AppFlow Logging'. I suspect there is a similar option for things other than the Netscaler Gateway if you're doing something else with your Netscaler.
... View more