Can't play via midi keyboard - but only one song!

Question

I am using logic 7 now for over a year. all my songs are ok.
but there is one single one on which I can't play keyboard notes on the
software instruments. it seems all midi events do not arrive at the song.
the transport window doesn't show any events. in the environment,
if I go to the "Input View" layer, I can see midi notes being received!!!!
but somewhere on the way they get lost.
that's strange as for all the other songs there's no problem at all.
so it must be something song specific. any ideas?
the input filter check boxes in the midi settings are not checked, btw.
thanks for any help, really appreciated, as it drives me nuts, I'd like to
finish that song...

Answer 1

You say this affects Audio Instruments; does that mean that if you use external devices, they play back okay?
If the note events are being received in the Environment, then it sounds like either they are then being routed away from the track you intended, or they are being muted.
First check for muted tracks, & then for soloed tracks (since these will mute all the others). Make sure you can see all the tracks & busses when you look!
Next, look at the input object which is receiving MIDI & see where it is routed. Unless it is routed to the track you want, you won't get the result you need. You can try switching it to another Audio Instrument to see if that makes a difference.
Also check inserts, in case you are (e.g.) gating the input!
I assume playback of previously-recorded tracks is not affected?
Do regions get created when you record (even though you can't hear anything), & if so, can you see note events when you inspect them in the editors?