Is there any reason that you don't do as perlsyn says and put an error check on your opens? 
open (LISTA, "find $folder -type f|")
  or die "Cannot find '$folder': $!";

[download]
That may or may not solve your immediate problem, but it definitely solves A problem...

And another thing, you are likely littering the process table with zombies. This may well be the cause of your loop crashing. You can either set a child handler, or you can start calling wait or waitpid to let your children exit. (If this guess is right then the error check should have noticed and pointed you in the right direction.)

UPDATE
I think I am wrong about the zombie guess. As mentioned below I suspect either memory corruption or a Perl bug. Using backticks to collect output may fix the program, but the bug should still be tracked down and reported.

In reply to Re (tilly) 1: Attempt to free unreferenced scalar... by tilly
in thread Attempt to free unreferenced scalar... by Daniellek

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