Use this javascript function with your textbox control onkeypress event
i.e. onKeyPress="return checkCharacters(event)" in CS
function checkCharacters(evt) {
evt = (evt) ? evt : window.event
var charCode = (evt.which) ? evt.which : evt.keyCode
if (charCode != 32 && charCode > 31 && (charCode < 65 || charCode > 90) && (charCode < 97 || charCode > 122)) {
status = "This field accepts numbers only."
return false
}
status = ""
var name = document.getElementById("txtloginID");
name.innerHTML = Server.HtmlDecode(name);
return true
}
hope this will help you thanks