Ajax not working in jsp

I'm using Netbean, Ajax validation in the following code is not working the code succesfully run for first UID validation adn also for ee-mail but does not enter if else for firstname field please help me out..

The files used are a zxml.js A IncrementalFormValidation.js

function validateField(oEvent) { oEvent = oEvent || window.event; var txtField = oEvent.target || oEvent.srcElement; var oXHR = zXmlHttp.createRequest(); oXHR.open("get", "ValidateForm.jsp?" + txtField.name + "=" + encodeURIComponent(txtField.value), true); oXHR.onreadystatechange = function () { if (oXHR.readyState == 4) { if (oXHR.status == 200) { var arrInfo = oXHR.responseText.split("||"); var imgError = document.getElementById("img" + txtField.id.substring(3) + "Error"); var btnSignUp = document.getElementById("btnSignUp");

            if (!eval(arrInfo[0])) {
                imgError.title = arrInfo[1];
                imgError.style.display = "";
                txtField.valid = false;                    
            } else {
                imgError.style.display = "none";
                txtField.valid = true;
            }

            btnSignUp.disabled = !isFormValid();
        } else {
            alert("An error occurred while trying to contact the server.");
        }
    }
};
oXHR.send(null);

};

function isFormValid() { var frmMain = document.forms[0]; var blnValid = true;

for (var i=0; i < frmMain.elements.length; i++) {        
    if (typeof frmMain.elements[i].valid == "boolean") {
        blnValid = blnValid && frmMain.elements[i].valid;            
    }
}

return blnValid;

}

//if Ajax is enabled, disable the submit button and assign event handlers window.onload = function () { if (zXmlHttp.isSupported()) { var btnSignUp = document.getElementById("btnSignUp");
var txtUID = document.getElementById("txtUID"); var txtFirstName = document.getElementById("txtFirstName"); var txtMiddlename = document.getElementById("txtMiddlename"); var txtLastname = document.getElementById("txtLastname"); var txtPhoneNo = document.getElementById("txtPhoneNo"); var txtEmailid = document.getElementById("txtEmailid"); var txtdobmonth = document.getElementById("txtdobmonth"); var txtdobday = document.getElementById("txtdobday"); var txtdobyear = document.getElementById("txtdobyear"); var txtselGender = document.getElementById("txtselGender"); var txtseloccupation = document.getElementById("txtseloccupation"); var txtYearlyIncome = document.getElementById("txtYearlyIncome"); var txtfile = document.getElementById("txtfile"); var txtAddress = document.getElementById("txtAddress"); var txtDistrict = document.getElementById("txtDistrict"); var txtfps = document.getElementById("txtfps");

    btnSignUp.disabled = true;
    txtUID.onblur = validateField;
    txtFirstName.onblur = validateField;
    txtMiddlename.onblur = validateField;
    txtLastname.onblur = validateField;
    txtPhone_No.onblur = validateField;
    txtEmailid.onblur = validateField;
    txtdob_month.onblur = validateField;
    txtdob_day.onblur = validateField;
    txtdob_year.onblur = validateField;
    txtselGender.onblur = validateField;
    txtseloccupation.onblur = validateField;
    txtYearly_Income.onblur = validateField;
    txtfile.onblur = validateField;
    txtAddress.onblur = validateField;
    txtDistrict.onblur = validateField;
    txtfps.onblur = validateField;
    txtUID.valid = false;
    txtFirstName.valid=false;
    txtMiddlename.valid=true;
    txtLastname.valid=false;
    txtPhone_No.valid =true;
    txtEmailid.valid =true;
    txtdob_month.valid=false;
    txtdob_day.valid=false;
    txtdob_year.valid=false;
    txtselGender.valid=false;
    txtseloccupation.valid=false;
    txtYearly_Income.valid=true;
    txtfile.valid=false;
    txtAddress.valid=false;
    txtDistrict.valid=false;
    txtfps.valid=false;


}

};

And a validateForm.jsp

<%@page contentType="text/plain" pageEncoding="UTF-8" import="java.util.regex.*,java.text.DateFormat" %> <%

//message output
String valid = "false";
String message = "An unknown error occurred.";    
if (request.getParameter("txtUID")!= null){
    if (request.getParameter("txtUID").length()==0){
        message="This field cannot be blank";
    }else{
    String uid= request.getParameter("txtUID");
    Pattern test =Pattern.compile ("[0-9]{12}$");
    Matcher m=test.matcher(uid);
    if (m.matches()){
        valid = "true";
        message = "";
    } else {
       message = "UID is 12 digits can only have numbers form 0-9";
      }
           }
} else if (request.getParameter("txtFirstName")!=null ){
    String fname= request.getParameter("txtFirstName");
    if(fname.length()==0){
        message="This field cannot be blank";
    }else {
     Pattern t=Pattern.compile("[A-Za-z]$");
      Matcher m1=t.matcher(request.getParameter("txtFirstName"));
      if (m1.matches()){
          valid="true";
          message="";
      }else{
          message="First Name can only contain text value";
      }
              }
} else if (request.getParameter("txtMiddleName")!=null){

} else if (request.getParameter("txtLastName")!=null){

} else if (request.getParameter("txtPhone_No")!=null){

} else if (request.getParameter("txtEmailid") != null) {
   if((request.getParameter("txtEmailid")).length()==0){
       valid="true";
       message="";
   }else{
   Pattern p = Pattern.compile("^[_a-z0-9-]+(\\.[_a-z0-9-]+)*@[a-z0-9-]+(\\.[a-z0-9-]+)*(\\.[a-z]{2,3})$");
   Matcher m = p.matcher(request.getParameter("txtEmailid"));

   if (m.matches()){
        valid = "true";
        message = "";
   } else {
       message = "This e-mail address is not valid";
     }  
   }    

} else if (request.getParameter("txtdob_month")!=null){

} else if (request.getParameter("txtdob_day")!=null){

} else if (request.getParameter("txtdob_year")!=null){

} else if (request.getParameter("txtselGender")!=null){

} else if (request.getParameter("txtseloccupation")!=null){                                            

} else if (request.getParameter("txtYearly_Income")!=null){

} else if (request.getParameter("txtfile")!=null){ 

} else if (request.getParameter("txtAddress")!=null){

} else if (request.getParameter("txtDistrict")!=null){

} else if (request.getParameter("txtfps") != null) {

}

%><%=valid%>||<%=message%>