[R] I source an R script. An error is reported. But on what line

[SHANE MILLER, BLOOMBERG/ 731 LEXIN]

> source("C:\\Documents and Settings\\smiller53\\Desktop\\perf.r")
Error in eval.with.vis(expr, envir, enclos) : element 1 is empty;
   the part of the args list of 'c' being evaluated was:

perf.r is a long script. how can I determine which line the error occurred on?

TIA, SHane