I’m posting this in the Cakewalk forums and EastWest forums in the hope that someone may have come across this and solved the problem. I searched both forums but didn’t come up with anything so far.
 
I’m working on some MIDI files that a friend bought from a library. The sound from his onboard GM set isn’t cutting it. I am using SONAR Platinum and EastWest libraries using the PLAY VST instrument. The problem could be coming from MIDI messages, possibly CC messages, but I’m not sure.
 
If I load the instrument up and play using my keyboard or clicking on the on-screen keyboard in PLAY, then the instrument works fine. As soon as the MIDI file is played, the sound disappears. The meter on the MIDI file track is responding and showing MIDI activity. If I use SONAR’s own TTS GM instrument, then it plays fine.
 
At first I thought the PLAY instrument wasn’t routing properly, but the meters in PLAY are responding, but with a very low output, around -37dB at the most. Resetting the track does not reset PLAY and the level stays low, even if I use my keyboard or the on-screen keyboard to send max velocity notes.
 
 
 
 
 
 
 
I checked the gains on the tracks in SONAR and they are all centred (set to zero???).
 
I tried copying the track to another MIDI track but this does not seem to fix the problem. Neither does looking into the event list and deleting CC messages one at a time to see if they are sending messages to PLAY.
 
I have also tried adding CC messages in the automation lanes to raise both the volume and expression controllers in case these are being turned down.
 
The really annoying thing is that it doesn’t happen on all instances of PLAY. I have several running, and the guitars and bass are fine, seemingly unaffected by this problem.  The problem is not restricted to PLAY either. I tried to use the Cakewalk SI-Bass Guitar plugin and had the same issue. I was able to get it working by changing the patch once the file started playing, but zeroing and playing the file again silenced the VST until I manually changed the patch again. I tried removing the bank and patch settings as well, but this made no difference.
 
So, anyone out there fancy helping me keep what little of my hair I have left in place? It may be something so blindingly obvious that it is right in front of my face, but it is bugging the hell out of me now.

Is your MIDI file trying to send patch changes at the start of each track?

IIRC I had this too, and deleted the SysEx data and patch changes on each track.

This is a well know issue with Cakewalk's sfz engine synths like SI-Bass Guitar. Third party MIDI files often contain instructions which cause the sfz engine to shut down. The files work in GM synths such as TTS-1 because it was programed to handle the instructions. Usually the offending data is at the beginning of the file. There are two ways to solve the problem, remove the data from the file using the Event List or instruct the synth to ignore the data by opening the Plug-in Properties and enabling "Do not intercept NRPNs." I do not know if the latter works for Play, I do not have the synth.

That above trick is one of a few things that you can try, 
 I have had this same issue for a long time and  so far have found there is no easy answer that always works. 
Here's a few tricks you can try.
1- Open the file in another DAW ( like Cubase)  and delete all the PG changes in the event list. There was even a freeware DAW I used to use but is not supported past XP. Anyhow this will work 100%.
2- Sonar PG messages do not show on the event list but look there anyways, you might get lucky.
3- Slip edit the track to the first note  which might eliminate a PG change at start of track.  
4- Use the track explorer and change the patch 
5- Try the synth properties dialog mentioned above but not all synths have that option, TTS-1 doesn't.
6- Change the tracks channel. The odd time this does work when combined with the slip edit trick,, have no clue why.

Thanks guys. I'll have a look at those solutions and come back if they are successful or not.

I also fixed the Bass Guitar problem by deleting the RPN data at the start of the track using the event list.
 
I also found that the bass in purchased files is usually 1 octave below what sounds and shows on the bass fretboard so if you transpose the bass track by +12 you will hear/see it. 

Thanks,
 
I have noticed the octave issue as well, but it wasn't that. I'll look at the RPN stuff later when I get home.

OK, I spent quite a while poking around at various things in PLAY and SONAR late last night. Just when I was about to give up at stupid o’clock in the morning I noticed that on the player screen, the filter light indicated that it was on and the frequency was swept right down. I turned it back up to full (100%) and… voila, sounds back to normal. The reason the output was so low was that only the low frequencies were getting through the filter. Once I turned the filter off it was no longer disappearing in the mix.
 
It was very late and I felt like I had managed a small victory so I left it there, I thought it might have been the Mod Wheel setting controlling the filter, so I attempted various edits the events and/or automation settings but to no avail. Although the filter was off and no longer affecting the sounds, I could see the frequency setting moving. I need to find what is controlling this for future settings. I also need to find out because I think it is also affecting PLAY when I use the Symphonic Choirs, and I can’t find the filter setting on the UI (if, indeed, it is even affected by it or whether this is a completely separate problem), I need more time to look at that.
 
So two questions –

1. Does anyone know which CC message or controller might be affecting the filter frequency setting in a standard, unaltered installation of PLAY?
2. Does anyone know of editing software (preferably free and simple for an old duffer like me) where I can edit events and/or controller messages? SONAR should be able to do it, but I feel like I’m missing something obvious.

Thanks again for taking the time here.

So, I followed a couple of suggestions from PLAY users over on the EastWest forums. I’d like to think it was as simple as going in to the track and finding the controller. However, SONAR seems to do a very good job of hiding this information. I noticed that for a couple of the affected tracks, there was an option for CC 74 in the automation lanes. A quick bit of googling and… hey presto! CC 74 is commonly used for adjusting VCF Cutoff frequency. I had already scoured the PLAY and Goliath manuals earlier today and there was no mention of this but it seems reasonable since that is what is happening.
 
Annoyingly, no matter how I try to alter the automation settings, either SONAR or PLAY are ignoring them and cranking the frequency down to its lowest setting. I have used the event editor to search each track for CC 74 messages, but nothing is showing there. I checked the piano roll view as you suggested and it’s not there either.
 
So, somewhere I suspect there is a CC 74 message altering the PLAY filter frequency, but SONAR is making it very difficult for me to find. It has identified that somewhere in the file CC 74 is doing something and has added it as an automation lane option, but I can’t alter it.
 
Still open to suggestions though! Oh, and thanks of course! 

Kind of a band-aid but you could insert a MIDI filter and remove CC-74 messages.