The name 'UserName' does not exist in the current context and The name 'Password' does not exist in the current context pls solve error

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C#

ASP.NET

SqlCommand cmd = new SqlCommand("select * signin where Username =@username and Password=@password", con);
cmd.Parameters.AddWithValue("@username", UserName.Text);
cmd.Parameters.AddWithValue("@password", Password.Text);
SqlDataAdapter da = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
if (dt.Rows.Count > 0)
{
Response.Redirect("Default.aspx");
}
else
{
ClientScript.RegisterStartupScript(Page.GetType(), "validation", "<script language='javascript'>alert('Invalid Username and Password')</script>");
}