This happened to me once before.  I was working along and suddenly all the channels on my Aria 64-bit player went dead.  Actually they were still playing but only at a whisper level.  I couldn't find any setting that cause this.  Even saving the project, shutting down SONAR and launching the project didn't get it back.  The only way I could restore the normal volume was by going into Aria, dropping the samples, and loading them again.  This it worked normally.
 
I went for a month without incident, even though I use the Aria player a lot.
 
Tonight I built a new project and this started happening again.  But this time, the instruments keep going away.  I am just editing the lengths of MIMI notes, and about every 10 seconds, the volume goes away.  I've probably had to reload these samples 15 times tonight.
 
Has this happened to anybody else?  I think I can run those same samples on Dimension, so I may try that next to see if it is an Aria problem.

I had some problems in the past with Aria - but it was mostly due to misunderstanding. I do know that Aria uses the mod wheel as a volume/expression control - they recommend not using CC 11 (expression) or CC 2 (breath) at the same time as things could get hairy.

The problems that I had were related to volume were having a CC 11 at the start of the midi I was using which would override the mod setting whenever I stopped. I also misunderstood the meaning of the 'zero controllers' setting in the project midi settings dialog. I learned a lot by examining the event list view and checking for codes which modify volume.
 
Another thing to check for is to make sure you don't have any automation which can modify things as well. In fact, having both automation and hard events in the event view can be a recipe for disaster - since both can modify the same parameters. (There is a way to take the midi controller events and import them into an automation lane...but that is another topic..)

SuperG
I had some problems in the past with Aria - but it was mostly due to misunderstanding. I do know that Aria uses the mod wheel as a volume/expression control - they recommend not using CC 11 (expression) or CC 2 (breath) at the same time as things could get hairy.

Thanks.  I'll look into that.  I imported the MIDI from an unknown Internet source and then was heavily modifying it.  It does see to have tome control events at the start of the file.  I think you have identified my problem.

I deleted all the controllers other than velocity and it still had this problem.  I gave up on that and switched over to Dimension Pro, which is working pretty well for the solo violin and cello lines I'm fiddling with (bad pun intended) -- and Dimension is not having any problem with that MIDI file.  I still think there is probably something in the MIDI that Aria doesn't like, but I can't mess with that right now, as this is for a funeral on a tight schedule.

Did you try freezing the synth? I say that because I had an instance where my ARIA would suddenly decide to play very loudly indeed, despite nothing being different. It would happen on the first or second playback for instance when other playbacks would be at the correct volume. Freezing the synth allowed me to guarantee the volume on playback.

Bibs

Thing only thing left it could be is automation if there's no midi codes modify it, or some cross wired patch in from another track.......
 
Next time you're free and you run into this, gives us a shout - I'm sure if I looked over the midi/project I could get to the bottom of it..

SuperG
Thing only thing left it could be is automation if there's no midi codes modify it, or some cross wired patch in from another track.......
 

Not that I can tell.  I did notice that one of the tracks (piano) has a continuous note all through the file -- the very bottom note on the MIDI piano scroll.  I couldn't hear that note.  I deleted it.  Maybe something like that was messing with Aria.  I didn't have any problem when running those same files into Dimension Pro.

SuperG
Next time you're free and you run into this, gives us a shout - I'm sure if I looked over the midi/project I could get to the bottom of it..

OK.  Thanks.

The mod wheel seems to always reset to 0 for some reason on Aria (for me).  This will control your volume, so make sure to put in a mod wheel event at the start of the track, or simply open the player and make sure it is up when you playback
 

LpMike75
The mod wheel seems to always reset to 0 for some reason on Aria (for me).  This will control your volume, so make sure to put in a mod wheel event at the start of the track, or simply open the player and make sure it is up when you playback 

Go into sonar prefs and uncheck reset midi controllers on stop. ( can't think of the exact phrase off the top of my head)
Voila, no more zero mod wheel etc.

Bibs

wizard71
Did you try freezing the synth? I say that because I had an instance where my ARIA would suddenly decide to play very loudly indeed, despite nothing being different. It would happen on the first or second playback for instance when other playbacks would be at the correct volume. Freezing the synth allowed me to guarantee the volume on playback.

I didn't freeze these tracks because I was in the process of editing the MIDI when the problem kept occurring.  If I had ever been able to finish editing, I am confident that freezing would have preserved the volume.  I freeze whenever I can because my system isn't very fast.