You need to add
"DefaultButton" property for the page.
ASP.NET 2.0 introduces a wonderful work around for your issue. By simply specifying the
"defaultbutton"
property to the ID of the
<asp:Button>
, whose event you want to fire, your job is done.
The defaultbutton property can be specified at the Form level in the form tag as well as at panel level in the
<asp:panel>
definition tag. The form level setting is overridden when specified at the panel level, for those controls that are inside the panel
Sample example:
<form id="Form1"
defaultbutton="SubmitButton"
defaultfocus="TextBox1"
runat="server">