ADO.NET: The ConnectionString property has not been initialized

You haven't passed a connection string to your connection object so it has no idea which database to open or where to find it.

Try this:

Dim con As New OleDb.OleDbConnection("My connection string") 

You are not giving the OleDbConnection object a connection string. The connection string tells the OleDbConnection object to which database you want it to connect. You can give it the connection string in the constructor, like this:

Dim con As New OleDb.OleDbConnection(connectionString) 

Or, you can set it afterwards, via the ConnectionString property, like this:

Dim con As New OleDb.OleDbConnection() con.ConnectionString = connectionString 

The format for the actual connection string varies depending on the database engine and version. There are plenty of resources online, though, which will show you the correct format to use and what options it can include. Just as an example, it might look something like this:

Dim connectionString As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=c:\MyDb.mdb" 

UPDATE

Sorry if I've confused you by discussing the steps out of order. Basically, all you need to do is to give the connection string to the OleDbConnection object. You need to do so before you call its Open method. For instance, you can change the following line:

Dim con As New OleDb.OleDbConnection 

To this:

Dim con As New OleDb.OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; Data Source=c:\MyDb.mdb") 

Obviously, however, you need to change the connection string to whatever it ought to be for your particular situation. The one above is merely an example of what a valid connection string looks like.

Or, if you don't want to give the connection string to the OleDbConnection object right away, you can wait to give it to it later, as long as you set it before calling Open. For instance, you could change the following lines:

Dim cmd As New OleDb.OleDbCommand Dim con As New OleDb.OleDbConnection Dim Printlist1 As New DataTable If Not con.State = ConnectionState.Open Then con.Open() ' ... 

To this:

Dim cmd As New OleDb.OleDbCommand Dim con As New OleDb.OleDbConnection Dim Printlist1 As New DataTable If Not con.State = ConnectionState.Open Then con.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=c:\MyDb.mdb" con.Open() ' ... 

The original example, which seems to have confused you, first stored the connection string in a variable, and then passed the value from that variable to the connection object, like this:

Dim connectionString As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=c:\MyDb.mdb" Dim con As New OleDb.OleDbConnection(connectionString)