I just happened to be sitting my computer (a consumer PC, not a workstation by any means) and I tried exporting a short clip using your settings and it worked fine. So it’s another one of those individual nuisance things, not a software bug.
I’m sure someone else will know what you can do to fix it. Preferences, re-install, hopefully for you something simpler. Anyway, just wanted to let you know you CAN export in quicktime using h264.