OK. Try the following in order to find out where the error resides.
Copy the following module into your cgi-bin directory and name it printenv (don't forget to make it executable):
#!/opt/lampp/bin/perl
##
## printenv -- demo CGI program which just prints its environment
##
print "Content-type: text/plain\n\n";
foreach $var (sort(keys(%ENV))) {
$val = $ENV{$var};
$val =~ s|\n|\\n|g;
$val =~ s|"|\\"|g;
print "${var}=\"${val}\"\n";
}
This module works fine in my xampp/cgi-bin environment.
Enter
http://yourdomain/cgi-bin/printenv
If you get nothing your xampp config files are incorrect.
If your xampp set-up is correct you should get the environment variables on your screen. In that case there is an error in the other cgi-bin modules you are using.