I've replied to this request over email, but let's cover it here, too -- in case anyone else bumps into a similar problem.

Support for Serial Tap Pro was added recently, in IO Ninja 5.8.0 -- therefore, please make sure that you are on a version higher than this. Generally speaking, you always want to be running the latest and greatest version of IO Ninja.

Also, on Windows, for Serial Tap Pro and other hardware sniffers to function correctly, the official hardware driver is required. This driver is actually nothing more than a manifest telling Windows to use the system winusb.sys for devices with our VID/PIDs (vendor and product IDs). Nevertheless, this step is essential -- without it, IO Ninja won't be able to communicate with the taps (and taps will have an exclamation mark in Windows Device Manager).

If you install IO Ninja via the "FULL" MSI installer, those drivers should be installed automatically. Otherwise (e.g., you prefer a portable .7z archive), please download drivers separately at Download -> IO Ninja Hardware Drivers; install them either (a) using dpinst64/dpinst32 or (b) through the standard Update Driver process in Device Manager.

After driver installation completes successfully, the taps in Device Manager should show no exclamation mark and use winusb.sys as a kernel-mode driver.