First off, I see that there are 2 occurrences of the Server Validation server behavior on the page.
In the list of server behaviors, select one of them and click the minus button to remove it.
Does the form successfully submit? Does it pass validation?
You have the insert record server behavior set to redirect to the index.php page, does this redirect occur?
another anomaly I see that the name of the page you have sent is "visitors_Registration2.php", but the failed validation redirect is "visitors_Registration3.php?invalid=true" so it goes to another page.
change the validation failure redierect to visitors_Registration2.php?invalid=true so that you are staying on the same page.