Thanks for the reply! I don't think it's a memory problem because it's a 64-bit machine, OS and Perl, and has 128G of memory installed. My stop-gap fix was to limit plotting to one less than the number that causes the exit, and I am able to plot 100 of those shorter lines, but not even one line that has one more sample. But your perl and Tk are both more recent versions than mine, and that might be part of it.