Update MySQL from .net with parameters

I have been having problems updating a MySQL database from c# code using parameters.

I have reduced it done to the code below.

This has the effect of updating the 'head' field with NULL

MySQL 5, Visual Studio 2010

I am populating strReturn with some info for debugging and I get this from it

update newsitems set head = @Head where id = 233 ; (command text)
@Head (parameter name)
Match Fees test (parameter value)
1 (rows affected)

Can someone tell me where I am going wrong?

      string strReturn = "";
      string strSql;
      string strHead = "Match Fees test";

      strSql = "update newsitems set head = @Head where id = 233 ;";

      using (MySqlConnection conn = new MySqlConnection(strConstring))
      {
        MySqlCommand cmd = null;

        try
        {

          conn.Open();

          cmd = new MySqlCommand(strSql, conn);
          cmd.CommandType = CommandType.Text;
          cmd.Prepare();

          cmd.Parameters.AddWithValue("@Head", strHead);

          strReturn += cmd.CommandText.ToString() + Environment.NewLine ;

          for (int i = 0; i < cmd.Parameters.Count; i++)
          {
            strReturn += cmd.Parameters[i].ParameterName.ToString() + Environment.NewLine;
            strReturn += cmd.Parameters[i].Value.ToString() + Environment.NewLine;
          }

          int intAffected = cmd.ExecuteNonQuery();
          strReturn += intAffected.ToString() + Environment.NewLine;

        }
        catch (Exception ex)
        {
        }
        finally
        {
          conn.Close();
        }
      }

      return strReturn;

Select allOpen in new window