how it can be solved?plz help me.thanx in advance

You can validate just before save.
what about using a javascript drop down calendar?

Regards
Sebastian

try like this:

$(document).ready(function() {
  $('#txtDate').blur(function() {
      if(validateDate('txtDate'))
      {
          alert('Date is valid');
      }
      else
      {
          alert('Invalid Date!!!');
      }
   });
});

//validation function Starts
function validateDate(txtDate){
   var txtVal = document.getElementById(txtDate).value;
   var filter = new RegExp("(0[123456789]|10|11|12)([/])([1-2][0-9][0-9][0-9])");
   if(filter.test(txtVal))
      return true;
   else
     return false;
}​
//Ends
//

Steps:
1. Add a onchanged client event to textbox on client side using Attributes.
2. Refer a JS function to the event
3. Pass textbox or textbox value to event method
4. Validate the data using regex or crude way

Something like:

TextBox4.Attributes.Add("onchange","javascript: ValidateMe(this);");

<script type="text/javascript">
// Will fire as soon as textbox looses focus after a change
function ValidateMe(curr) {
   //    alert(curr.value);
   // use the value and validate it
}
</script>