Midi/Soft Synth problem

Hello everyone.
 
I'm having a problem with my soft synths, possibly related to midi with Sonar X1.
 
When I change instruments in Dimension Pro, rapture, etc., most of the time, I will get no sound after that when I try playing the instruments from my midi controller.  When that happens, True Pianos can't be played by clicking on its virtual keyboard either.  There is no sound and nothing is showing up on the meters.  Sometimes, if I click the play button in the transport bar, and then stop playback, I can then play the instruments again, but sometimes even that won't work and I have to close Sonar X1 and restart it to be able to hear the instruments again.  The same problem happens even if I don't change instruments if I have been playing with Session Drummer for a short while.  Also, I wrote in notes in another project in the staff view.  For awhile, playback of those notes would play the instruments, even if I couldn't play the instruments with my midi controller or with the virtual keyboard of True Pianos.  But now, on playback of the written notes, each track will play a few notes, then stop.  Session Drummer will play a few beats, then stop, then start again.
 
I run into the same problems if I don't even turn on the midi controller and just play with the synths in Sonar by virtual keyboard in True Pianos and playing with Session Drummer 3.
 
My system is a 4-month old Dell, i7 with 12 GB ram.  I have installed both a and b patches to Sonar X1, but not the new quick fix.  My interface is the Echo Layla 3G, with the latest drivers, using ASIO.  My midi controller is the Studio Logic SL-1100.  I have set Sonar to send control off messages to the midi controller.
 
I'm am not getting any dropout messages.  Memory usage is about 10%, hard drive usage is less than 30%, the first processor is showing under 30% usage, the other processors much less than that.
 
I tried increasing the various buffers, but that doesn't seem to make a difference.
 
Any ideas to try?
 
Doug