I found the solution using simple javascript isValid property
What I am doing is checking for the validity of all the validators, if all validators are correct and passed then only I am calling block ui to block the login form as follows:`
$(document).ready(function () {
$('#btnCustLogin').click(function () {
if (document.getElementById("rfvCustEmailID").isvalid && document.getElementById("revCustEmailID").isvalid && document.getElementById("rfvCustPwd").isvalid) {
$('div#LoginForm').block({
message: '<h3><img src="Images/Loading_Smaller.gif"/> Processing...</h3>',
css: {
border: '3px solid #35a7c1',
width: '200px'
}
});
}
});
});
Now the login form is blocking only when the all validators are passed and remain blocked until the server side validation completed and update panel updates.