How can I fix this issue?

See more:

C#

ASP.NET

This is the code of my master page, and here i placed a logout button click event that do the stuff. i applied this master page on different .aspx pages. My problem is that when ever i press enter button on that every aspx page, it logges me out from my website. did i made any mistake? Help me soon...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;

public partial class UserMasterPage : System.Web.UI.MasterPage
{
    SqlConnection con = new SqlConnection("Data Source=.\\sql2008;initial catalog=ProductivePlusDB;user id=sa;password=123456");
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["emailid"] == null || Session["emailid"].ToString() == "")
        {
            Response.Redirect("Default.aspx");
        }
        string qry = "select *from ShopOwnMast where EmailId='" + Session["emailid"] + "'";
        con.Open();
        SqlDataAdapter adp = new SqlDataAdapter(qry, con);
        DataSet ds = new DataSet();
        adp.Fill(ds);

        if (ds.Tables[0].Rows.Count > 0)
        {
            if (!IsPostBack == true)
            {
                lbluname.Text = ds.Tables[0].Rows[0][1].ToString();
            }

        }

        
    }
    protected void btnLogOut_Click(object sender, EventArgs e)
    {
        Session.Abandon();
        Response.Redirect("Default.aspx");
    }
}

This is the logout button code in that master page:

<div class="top-menu">
               <ul class="nav pull-right top-menu">
                    <li><asp:Button Class="btn btn-theme04" ID="btnLogOut" runat="server"
                           Text="Log Out"
                           style="color:White; margin-top: 15px; margin-left:10px "
                            onclick="btnLogOut_Click" TabIndex="10"></asp:Button></li>
               </ul>
           </div>

What I have tried:

I placed TabIndex ="10" for the solution but it didnt works

i thing this button is selected as default.
i don't have any idea how to fix it.