I notice that your ReadFile subroutine reads an entire file into memory. Your 'Out of Memory' message might be concerned with that, rather than forks and threads. Although there are a number of places where you fork child processes (date, awk, rm) unnecessarily, I doubt you would get that particular error message. Are the files being read on each machine exactly the same size?

A good move would be to trace when the program is executing when it crashes. If you do that, make sure you print to STDERR (or maybe use warn) in case messages are lost through buffering.