ANE has recently started throwing error #3500 in Flash CC

I have been using the same ANE for about 18 months now for native alerts in AIR on Windows desktop. Just recently AIR has started throwing the following error when trying to call any of the functions in the extension (in this example confirm is the function being called in the NativeDialog ANE):

ArgumentError: Error #3500: The extension context does not have a method with the name confirm.

  at flash.external::ExtensionContext/_call()

  at flash.external::ExtensionContext/call()

  at com.nemenvisual::NativeDialog/confirm()

  at application.ui::NativeAlert$/confirm()

  at application.control::CommandCentre$/execute()

When the app is published and installed it seems to work fine - the error only occurs when debugging in Flash CC. Has a recent update to Flash introduced this or is there some way around it? I tried going back to AIR 14 and the issue still occurs so I don't think an AIR update has caused it.