# pragma
use strict;
use warnings;

# modules
use XML::Simple;
use XML::Tidy;
use Data::Dumper;
use Data::Diver qw( Dive DiveRef DiveError );
use HTML::TreeBuilder;
use XML::Tidy::Tiny;

# little helper
use constant false => 0;
use constant true => 1;

...

        # get instance of treebuilder
        my $root = HTML::TreeBuilder->new();
        # configure treebuilder
        $root->ignore_unknown( false );
        # dump data to the treebuilder
        $root->parse( $fileData );
        # get name for target file
        my $target = $file;
        $target =~ s/$fileExtension$/xml/;
        # open output filehandle
        open( $FH, '>', $target );
        # configure output
        binmode $FH, ":utf8";

        # ERROR HERE
208:    my $data = $root->guts()->as_XML();

        print $FH xml_tidy( $data );
        close $FH;
...