Hi there,
 
You seem to be trying to open a new reference to a resource that has already been reserved every time you execute the while loop.
Error -50103 is a resource reserved error. (If you go to Help>>Explain Error and in the dialogue box input the full error, you will get an indication of the problem.)
I would also try highlight execution.
 
I would suggest that you take all of the configuration vi's outside of the while loop.  You only ever need to update the channel names and frequency once.
 
See attached:
 
Hope this helps
 
AdamB


PWM.JPG:
http://forums.ni.com/attachments/ni/...2083/1/PWM.JPG