At my school all the flash programs use those 3 keys as the new frame, keyframe and blank frame shortcuts. Its just a tad irritating going up and selecting which frame to add over and over again for a 500+ animation. Help meh!
These shortcuts still work in Flash CC. Can you share your machine/OS details and the Flash version.
Please also check your keybpard shortcut settings to see if they are correctly set or not (Edit menu > Keyboard Shortcuts > Under Timeline commands).
Try resetting your Flash preferences and retry.