Communicating with Zebra GK420d through Zebra OPOS driver

Question

Hi there, I am using a Zebra GK420d label printer for a POS application that i am developing. I am trying to communicate with the printer through its OPOS drivers provided by Zebra. But i get into trouble. It is a simple form in visual basic 2008 with a button on it. Here is the complete code that i am running.

Public Class FrameStep1 Inherits System.Windows.Forms.Form

Private m_Printer As Microsoft.PointOfService.PosPrinter = Nothing

Private Sub ChangeButtonStatus()

    'Disable control.
    btnPrint.Enabled = False
End Sub

Private Sub FrameStep1_Load(ByVal sender As System.Object _
, ByVal e As System.EventArgs) Handles MyBase.Load

    Dim strLogicalName As String
    Dim deviceInfo As DeviceInfo
    Dim posExplorer As PosExplorer

    strLogicalName = "zebra"
    posExplorer = New PosExplorer

    m_Printer = Nothing

    Try
        deviceInfo = posExplorer.GetDevice(DeviceType.PosPrinter, strLogicalName)
        m_Printer = posExplorer.CreateInstance(deviceInfo)

    Catch ex As Exception
        ChangeButtonStatus()
        Return
    End Try

    Try

        m_Printer.Open()
        m_Printer.Claim(1000)
        m_Printer.DeviceEnabled = True

    Catch ex As PosControlException

        ChangeButtonStatus()

    End Try
End Sub


 Private Sub btnPrint_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPrint.Click

    Try

        m_Printer.PrintNormal(PrinterStation.Receipt, "Hello OPOS for .Net" + vbCrLf)

    Catch ex As PosControlException

    End Try
End Sub

Private Sub FrameStep1_Closing(ByVal sender As Object _
, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing

    If m_Printer Is Nothing Then
        Return
    End If

    Try
        m_Printer.DeviceEnabled = False
        m_Printer.Release()
    Catch ex As Exception

    Finally
        m_Printer.Close()

    End Try
End Sub

End Class

You can see that i have called claim() and set DeviceEnabled=true. However, when i debug it what happens is as the control passes over m_Printer.Open() it magically ends up in btnPrint_Click() and does not go any further unless i click the button on my form and then at m_Printer.PrintNormal() it breaks and throws POSControlException and the text therein reads "An attempt was made to access an exclusive-use device that must be claimed before the method or property set action can be used."

Do I seem to be doing anything wrong here.