"Connection was not closed. Connection's current State was open"- Ms Access Visual Basic- Visual Studio 2010 - vb.net

Question

My connection between my project and my Ms Access 2010 Database seems to be right at the moment of logging in with my project. However, After the first trial(if user and/or password are incorrect), when I try to log in again, the error is given. It says "Connection was not closed. Connection's current State was open". I just have found possible solutions for MySql service, but I'm using Ms Access database. The code where the error seems to be given is the following. Any suggestions?, please:
Public Function Validation()
da.Fill(dt)
connection.Open()
For Each DataRow In dt.Rows
If txtUser.Text = DataRow.Item(0) And txtPassword.Text = DataRow(1) Then
If cmbAccountType.Text = DataRow(2) Then
connection.Close()
Return True
End If
End If
Next
Return False
End Function

Answer 1

Why are you opening the connection in the first place? You're not using it between the Open and Close calls so what's the point? The Fill method will automatically open the connection if it's currently closed and then it will automatically close it again if it opened it, i.e. Fill and Update will open the connection if necessary and then leave it in its original state afterwards. Get rid of both the Open and Close calls.

Answer 2

To begin with, Function's in vb.net require a DataType. I have no idea what da.Fill(dt) is doing in this function. If you didn't have an open connection you wouldn't be able to fill anything but then on the next line you open some unknown connection from somewhere.
OleDb pays no attention to the names of parameters. The position of the parameters in the sql string must match the order that the parameters are added to the parameters collection.
Here is one approach.
Private ConnStr As String = "Your connection string"
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If Validation(txtUser.Text, txtPassword.Text, cmbAccountType.Text) Then
'Do something
End If
End Sub
Public Function Validation(UName As String, PWord As String, Type As String) As Boolean
Dim Count As Integer
Using cn As New OleDbConnection(ConnStr),
cmd As New OleDbCommand("Select Count(*) From SomeTable Where User = #User And Password = #Password And AccountType = #Type;", cn)
cmd.Parameters.Add("#User", OleDbType.VarChar).Value = UName
cmd.Parameters.Add("#Password", OleDbType.VarChar).Value = PWord
cmd.Parameters.Add("#Type", OleDbType.VarChar).Value = Type
cn.Open()
Count = CInt(cmd.ExecuteScalar)
End Using
If Count > 0 Then
Return True
End If
Return False
End Function
Of course you should NEVER store passwords as plain text.