Ho un classe compilata

Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.HtmlControls

Namespace MyComponent

Public Class MonitorAgente
Public Sub New()
ExecuteConnection
End Sub

Private Sub ExecuteConnection
Dim strConString As String
strConString = "Server=*.*.*.*;UID=*******;PWD=********;Database=******"
_conDb = New SqlConnection( strConString )
_strSelect = "Select * from Employees"
_conDb.Open()
_conDb.Close()
End Sub

Qualcuno mi sa dire come mai quando la istanzio ed eseguo il comando mi da come errore questo:
System.TypeLoadException: Formato dei metadati PInvoke non valido
Se tolgo _conDb.Open() non genera errore, ma non fa neanche niente