I have occasional trouble manually playing soft synths from a master keyboard. A pre-recorded midi track is played back fine (using Dimension for example), and during that playback I can access the synth and play it just fine.
As soon as the playback track is stopped, I can see that i am sending midi activity to the correct synth output but no sound is heard. I have checked the obvious, (I hope),
but any youse folks experiience this? Audio Engine issue? Sample rate difference. I looked at all the midi ch. assignments and they appear to be OK. Man this grinds my gears!
I'd rather be fighting a life size chicken...
Thanks.     

The things needed are 
 A blank midi track or one your going to play over and erase.
That track has the following attributes. 
Input set to the MIDI in port of your interface or the USB device used for input. Use Omni mode. 
Output set to the desired soft synth and channel. 
Focus set to the track and the pink echo icon lit. 
 

Yup, check on all of those! Dag nab it...I'll find it,  thanks for the response.
 

So you have one track playing back a pre-recorded MIDI track on Dimension Pro for example and a second MIDI track assigned to another softsynth different from the  other track and its not playing after the piece finishes?  
 
I'd look at the Event List on the pre-recorded track. Sometimes people put in Volume controls at the end of a track that turn the volume all the way down. 

Under Project Options, MIDI Out there is a tic box to Zero controllers when play stops. I keep this
un-ticed on all my MIDI stuff. I use Sonar in live band situation to control a B4 and every now and then
Sonar seems to lose the controller. I'm banging on the keys, the MIDI interface is flashing, but
 the B4 won't play. I usually have to reload the project to get it working.
 
DaveT