COBOL instrumentation in Visual Studio

I am tasked with trying to find ways to improve performance of Visual COBOL application.  The Visual Studio Instrumentation appears to match to symbols from COBOL code for some functions, but in many cases can not match source.  I tried to VS Premium 2013 and VS Premium 2010 and get similar results to below.

The "Summary" of instrumentation process will show long running Functions, but when selected it will display "Source code not available.  You may not have the appropriate symbol paths or there was an error loading symbols.".  I have double checked the symbols path.  Is there any known issues with using VS Intrumentation?  Any suggestion for determining which functions in our COBOL app are taking most of the time?