ur missing objcommand.ExecuteNonQuery(); and parenthesis in code try this one

<script runat="server">
protected void CreateUserWizard1_CreatedUser(object sender, EventArgs e)
{
System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection();
string connectionstr=@"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\EHSAN\Documents\Visual Studio 2010\Projects\The Club\The Club\App_Data\Database1.mdf;Integrated Security=True;User Instance=True";
con.ConnectionString=connectionstr;
string sqlstring;
sqlstring ="insert into Authenticate (username,password)VALUES ('"+ CreateUserWizard1.UserName+"','"+CreateUserWizard1.Password+"')";
System.Data.SqlClient.SqlCommand objcommand = new System.Data.SqlClient.SqlCommand(sqlstring, con);
Con.Open();
objcommand.ExecuteNonQuery();
Con.Close();
Response.Redirect("~/Login.aspx");
}
</script>
<asp:Content ID="Content1" ContentPlaceHolderID="cphMain" Runat="server">
<asp:CreateUserWizard ID="CreateUserWizard1" Runat="server"
oncreateduser="CreateUserWizard1_CreatedUser">
</asp:CreateUserWizard>
</asp:Content>

is it possible to check e.Cell.ForeColor in if then ur problem may solve.. try it for example and u have store this booked dates in database ..use this link for help http://msdn.microsoft.com/en-us/library/ms228044(v=vs.90).aspx[^]

protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)
{
//do databse connectivity
//run while loop store this fromdate and todate in two variable
//do same thing as u have done to display in red fore
if (e.Day.Date < DateTime.Today)
{

e.Day.IsSelectable = false;
e.Cell.ForeColor = System.Drawing.Color.Gray;
}
else
{
if(e.Cell.ForeColor != System.Drawing.Color.Red)
e.Cell.ForeColor = System.Drawing.Color.Green;
}
if (e.Day.Date >= FromDate && e.Day.Date <= ToDate)
{
e.Cell.ForeColor = System.Drawing.Color.Red;
}
}

it is working!!!!!!....have u set dropdownlists autopostback property to true...for this code it is required

try this .First get from and to date in two variable then compare them

protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)
{
DateTime FromDate =Convert.ToDateTime(ddlFrom.SelectedValue);
DateTime ToDate =Convert.ToDateTime(ddlTo.SelectedValue);

if(e.Day.Date >= FromDate && e.Day.Date <= ToDate )
{
e.Cell.BackColor = System.Drawing.Color.Red;
}
}