Required Connection that are open and available. The current state of the connection is closed.

C # using OLE DB to manipulate access
Provider=Microsoft.Jet.OLEDB.4.0;Data source= "+ NewFileName +"; User Id=uid; Jet oledb:database password=pwd; ";

Complete error message:
{System.InvalidOperationException:ExecuteScalar requires a Connection that is already open and available. The current state of the connection is closed.
In System.Data.OleDb.OleDbConnection.CheckStateOpen (String method)
In System.Data.OleDb.OleDbCommand.ValidateConnection (String method)
In System.Data.OleDb.OleDbCommand.ValidateConnectionAndTransaction (String method)
In System.Data.OleDb.OleDbCommand.ExecuteReaderInternal (CommandBehavior behavior, String method)
In System.Data.OleDb.OleDbCommand.ExecuteScalar ()
In Public.DB.CheckTableIfExist (string tablename, string condition) position Public\db.cs: line number 136
In Myini.getcompanyname () position Program.cs: line number 293
In Program.main () position Program.cs: line number 734}

cause of error:
The current state of the connection is closed. or only the connection object is created, no call is made to
Connection.Open () method;
namely: Connection. State! = connectionstate.closed

Workaround:
Call the Connection.Open () method;
Or add a judgment, such as the following code:

if (MyIni.Gs_con.State != ConnectionState.Closed) {     new OleDbCommand(sqltext, MyIni.Gs_con);     //tools.MB(sqltext);     result = tools.fieldnullint(mysc.ExecuteScalar());     if0returnfalse; }

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Required Connection that are open and available. The current state of the connection is closed.