I messed up an edit on a track, so I deleted that track.

I would now like to create a new track and drop a clip from the bin onto the newly created track.

If I go to 'timeline', I can create tracks of various kinds.
However, what I can't do is drop a clip into that track.

The track is an mp4 file which contains both audio and video.

When I try to drop the clip onto a newly-created track, the image of the clip that I'm dragging just dissapears and the track has not been altered.

because the new video track you have created is maybe V4.... but there is not an A4 audio track on the timeline... A/V clips can't be dropped on a track if the track is NOT an A/V tarck (this mean: A1-V1 .... A5...V5

you have just to create an audio tarck with the same number of the V track.