Taking UserId from membership and storing in a table

Question

namespace Supportticketsystem.Admins

{

    public partial class WebForm1 : System.Web.UI.Page

    {

        

        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["TicketConnectionString"].ConnectionString);

        protected void Page_Load(object sender, EventArgs e)

        {

            con.Open();

        }

        protected void btnSend_Click(object sender, EventArgs e)

        {

            Session["UserLoginName"] = User.Identity.Name;

            string ticketstatus = "Pending";

            string userid = Membership.GetUser(HttpContext.Current.User.Identity.Name).ProviderUserKey.ToString();

            SqlCommand cmd = new SqlCommand("Insert into Ticket(Type,Department,Category,Title,Detail,CreatedBy,CreateDate,UserId,CurrentStatus,CurrentStatusDate,LastUpdatedDate,LastUpdatedBy,RoomNo,Availabilty) values('" + ddlType.Text + "','" + ddlDepartment.Text + "','" + ddlCategory.Text + "','" + txtSubject.Text + "','" + txtMessage.Text + "','" + txtName.Text + "','" + userid + "','" + ticketstatus + "','" + DateTime.Now + "','" + Session["UserLoginName"] + "','" + DateTime.Now + "','" + txtRoom+ "','" + ddlAvailability.Text + "')", con);

            cmd.ExecuteNonQuery();

            con.Close();

            Label4.Visible = true;

            Label4.Text = "Data inserted successfully";

        }

       

    }

}

The above code is running good but "string userid = Membership.GetUser(HttpContext.Current.User.Identity.Name).ProviderUserKey.ToString();" line is showing error. It says "  string userid = Membership.GetUser(HttpContext.Current.User.Identity.Name).ProviderUserKey.ToString();" 

kindly help me out.  

In above example I want to store information from textboxs, dropdownlists etc and also need UserId and UserName. Which I am trying from membership. Show the correct form of doing this pls. Also suggest if there is a better way.