Inserting a record into sql2005

Hi,

 I am having a difficult time trying to insert a record into sql2005 with data from a web form.  When using the following code below I get and error: Must declare the scalar variable "@tb_tripno". So I typed in: myCmd.Parameters.AddWithValue("TripNo", @tb_tripno) and the error is replaced by a different error: No mapping exists from object type System.Web.UI.WebControls.TextBox to a known managed provider native type.

I know the connection to the database is good because ...