How should 'programming error' messages be tracked

[Edward Sanford Sutton, III]

  I get a lot of 'programming error: Infinity or NaN encountered while 
converting Real number; setting to zero. (Continuing; crossing fingers)' 
messages sometimes in the Chompin piece I've been typesetting. I think it 
could be related to grace notes when they are in some tight measures, but the 
error doesn't state what measures the problems occur in or where in the lily 
file they relate to.
  Running with --verbose leaves the 'programming error' messages as they were, 
but brings out other details (and warnings) related to other parts of the 
processing.
  I would be grateful for any advice and I'll provide any other desired 
details if necessary.
Thanks again,
Ed Sutton