Hi Nan
thanks for your reply, I got it resolved I have added the following Page_ISValid in the script
<script type="text/javascript">
function validate() {
if (!Page_IsValid) {
return false;
}
if ($(".ajax__fileupload_fileItemInfo").length > 1) {
alert('only 1 File is allowed to Upload');
}
else {
alert('Select thesis file (only .pdf) to upload it');
}
}
</script>