Why does "Add RTX® support for a cifX device" not work

This could be a problem with the RTX Pnp Device Settings Dialog from RTX.
Instead of using the <OK> button, use the <Apply> button to confirm changes.

Please follow the link to the IntervalZero page describing the procedure.

https://www.intervalzero.com/library/RTX/WebHelp/Content/PROJECTS/Subsystem/Managing_Devices/Converting_a_Windows_Device_to_an_RTX_Device.htm