[suicune]

You're recording MIDI directly onto instrument tracks yes? Occasionally you may find when you close a session and reopen it Pro Tools will have lost its MIDI routing. This will often happen after a crash, or when your MIDI studio setup has changed in between closing and opening, or sometimes it seems to happen for no reason at all.

It can be fixed though. If you've still got the broken session open it so you can have a go. Go to View>Edit Window Views and make sure 'Instruments' is checked on. Now look for the column instruments next to your track header and scroll to one of the greyed out tracks. It will show a MIDI input, which will normally be 'All', and a MIDI output either below or next to the input depending on the track height. You should find on a broken track this is in italics and a different shade which indicates an inactive output. Now if you open the instrument plugin window for that track in the top left hand corner it will say 'MIDI node' which will tell you what port the plugin should be on. For example the 2nd Xpand2 plugin in your session would be 'Xpand2 2'. Now click and hold on the greyed out output assignment. It will bring up a list of available MIDI nodes. In the example above you would be selecting 'Xpand2 2>channel 1' from the list. You should then see the tracks regions revert to blue. Repeat the process for all the broken tracks.

A much faster way of doing this that will work 99% of the time is to simply drag the plugin instrument from its current insert slot to a different one. This will force PT to re-assign the MIDI channel. Having said that, I definitely think it's worth learning how to manually reassign ports if you intend to be working with MIDI a lot.

On a side note, I always work with separate MIDI tracks which are routed to instrument channels instead of recording straight onto an instrument track. There are a number of advantages to this - eg 1) If you've got your IO view on all the time you can see straight away when the routing has broken, and repair it without having to change the view settings. 2) You can have multiple MIDI tracks going to the same instrument if you want more than one part to use the same sound. 3) You can set up mirrored outputs if you want the same part to play multiple instruments.

Hope that makes sense!