Key Mode lets you jump directly between keyframes in your animation. By default, Key Mode uses the keys visible in the track bar below the time slider. Other options are available on the Time Configuration dialog in the Key Steps group.
When the Auto Key button on and you change an object’s creation parameters or performed a transform, or change a material or modifier applied to that object, 3ds Max automatically creates a keyframe.
Key Mode can respect all keyframes, or you can restrict it to move only to transform keys via the Key Steps options on the Time Configuration dialog. When Key Steps Use TrackBar is on, Key Mode jumps to keyframes of any type. When Use TrackBar is off, Key Mode respects only transform keys.
If the current frame does not jump to the keys, make sure the animated object is selected in the viewport.
If it still doesn’t seem to be working, configure Key Mode to Use TrackBar, as described in the following procedure.
If you turn on Use TrackBar and turn Key Mode on, then clicking Next Key advances to the next key for the selected object. This will respect every type of key that appears in the track bar. If you turn Use TrackBar off, only transform keys are used by key mode.