This is because in your Page_Load you are loading only employeeid, so your data table gets created with just that one column. Then in the btnadd_Click you are trying to set the FirstName and LastName columns to some values. But those columns don't exist in the table. Depending on what you want, one way to fix it would be to add the two columns to your Page_Load
....con.ConnectionString = ConfigurationManager.ConnectionStrings["north"].ConnectionString;
com.CommandText = "select employeeid,FirstName, LastName from employees order by employeeid";Taht assumes that the employees table in the database has those two columns with those names.