in ascx page i have added a cutom button as follows

xrx:CustomButton id="CustomButton4" runat="server" OnClientClick="Login" Text="Login" />

in ascx.cs i have

protected void Page_Load(object sender, EventArgs e) {

    CustomButton4.OnClientClick = Page.ClientScript.GetPostBackEventReference(this.CustomButton4, string.Empty);
    this.lblAppName.Text = this.AppName;
    lblsession.Text = this.GetString("SDE_SESSION_EXPIRED_PLEASE1");

}


protected void Login(object sender, EventArgs e)
{
    Xerox.FMP.Providers.FormsAuthentication formsAuthHelper = new Xerox.FMP.Providers.FormsAuthentication();
    formsAuthHelper.SignOut();
    Response.Redirect("~/LoginPage.aspx", true);
}

when i click on login button the page is not redirecting to loginpage.aspx instead it is throwing an error object expected.

Can you please help me with this issue.