What does

can't get the value of $filename into that path ... or something like that

mean?

Change

open (XMLFILE,">c:/Perl_Tests/".$filename.".xml");
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to

my $path = ">c:/Perl_Tests/".$filename.".xml";
open (XMLFILE, $path) or die "Opening $path : $!";
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Then you can see what error ($!) caused the open to fail (as well as the path that was used).

You should also add use strict; use warnings at the top of your program.