Problem: Say you have two Grid View controls on one page, each grid view has a TexBox and a 'search' button above it
TextBox1 btnSearch1 TextBox2 btnSearch2
Now if you press 'Enter' key in TextBox1, it will trigger btnSearch1_click event and when you press 'Enter' key in TextBox2, it still triggers btnSearch1_click
Solution: Add asp.net Panel tag and set DefaultButton property.
<asp:Panel ID="pnlSearch2" runat="server" DefaultButton="btnSearch2">
TextBox2 btnSearch2
</asp:Panel>