sub fix_special_characters {
    my($string) = @_;
    
    open(C,"<:utf8","chars.txt");
    my @c = <C>;
    chomp @c;
    
    for my $i (0 .. $#c) {
        my ($special, $htmlchar) = split /\s+/, $c[$i];
        print "$special : $htmlchar\n";
        $string =~ s/$special/$htmlchar/ig;     ## this is generating the error message
    }
    
    return $string;
}