Finding out of bounds error

FROM : Modesitt Software
DATE : Wed Apr 06 01:58:15 2005

When running my application, the run log window displays this text in
red:

2005-04-05 16:44:47.614 MyRoutine[1615] *** -[NSConstantString
characterAtIndex:]: Range or index out of bounds

What does the number [1615] after MyRoutine mean?
Is there a way to get the debugger to stop when the out of bounds
occurs?  I'm having a hard time determining where in my code this
happens.
Thanks in advance!
Bill