Hi guys!

i've got this asp.net page that calculate 2 integer and add both of them to get the new value and it is working. Now i want to add in a validation that check for the 1st textbox to see if it is empty or not. If it is empty then it will pop out a msg saying that it is empty. I think i did it correctly buy it seems to show an error when i try to run it. I will attach the code here and please have a look.

Code:
<%@ Page Language="VB" %>
<html>
<script language="vb" runat="server">
	Sub SubmitBtn_Click(Sender as object, E as EventArgs)
		if text1.text = "" then
		msgbox("empty")
		else
			result.Text = val(Text1.text) + val(Text2.text)
		end if
	End Sub
</script>
<head>
<title>Calculation</title>
<link rel="stylesheet"href="intro.css">
</head>
<body>
<center>
<form action="calulate.aspx" method="post" runat=server>
<h3> Number 1: <asp:TextBox id="text1" runat="server"/>
	 Number 2: <asp:TextBox id="text2" runat="server"/>
</h3>
<p>  <b>Answer Is:</b> <asp:TextBox id="result" runat="server"/>
</p>
<p>  
  <asp:Button text="Calculate" onClick="SubmitBtn_Click" runat="server"/>
</p>
</form>
</center>
</body>
</html>
can any 1 help me solve this problem? I'm still learning asp.net. THe validation check i did is in

Code:
Sub SubmitBtn_Click(Sender as object, E as EventArgs)
		if text1.text = "" then
		msgbox("empty")
		else
			result.Text = val(Text1.text) + val(Text2.text)
		end if
	End Sub
with the if else statement. Please have a look and help me. Thanks.