Change line 45 to

open OUT, '>', $filename or die ">$filename< error - $!";
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Now you can see what filename gives you problems. More likely than not you will see it is an invalid filename (such as containing a linefeed or other illegal character).

PS1: I also changed your open to the three arguments variant. It would even be better if you use lexical variables as filehandles.

PS2: This script is not really "State of the Art", I guess it must be rather old already or based upon an old script, so try not to pick up too many bad habits by studying it.