Unable to export X4 mp4 files

Can someone tell me why I am unable to Export X4 mp4s from Studio? I have the current version of Studio on a laptop. I do my work on a Win 10 laptop and work on editing clips in the media area. When I make what I want to Export Studio does not allow me to Export that X4 mp4. I've sure had a lot of troubles with X4. X3 files work great in Studio.

Need to figure out how to Export X4 mp4s.