add a reference to System.Data.dllthen at the top of your cs file, add:using System.Data;
using System.Data.SqlClient;C# is case-sensitive, change
sqlDataReader reader1=sqlSelectCommand1.ExecuteReader();
==>
SqlDataReader reader1=sqlSelectCommand1.ExecuteReader();
using System.Data.SqlClient;C# is case-sensitive, change
sqlDataReader reader1=sqlSelectCommand1.ExecuteReader();
==>
SqlDataReader reader1=sqlSelectCommand1.ExecuteReader();
using System.Data.SqlClient;