Write a small test program

#!/usr/bin/perl    
use strict;
use warnings;
use CGI qw(:standard);  
use CGI::Carp 'fatalsToBrowser';
 
my $dir = "c:/inetpub/wwwroot/data"; 

print header('text/plain');
if ( open my $fh,'>',$dir.'/write.txt' ){
  print "OK : write.txt created in $dir";
  close $fh;
} else {
  print "ERROR : No write permission to $dir"
}
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Much better. Solved the rights issue. In Anonymous Authentication switched from "Specific User" to "Application pool identity". Thanks all!!!