Zebra GK420d Communication Using Zebra OPOS Driver

I am using a Zebra GK420d label printer for a POS application I am developing. I am trying to communicate with a printer through its OPOS drivers provided by Zebra. But I'm in trouble. It is a simple form in Visual Basic 2008 with a button on it. Here is the complete code 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 called claim () and set DeviceEnabled = true. However, when I debug what is happening, since the control goes through m_Printer.Open (), it magically ends up at btnPrint_Click () and doesn't go any further unless I click a button on my form and then on m_Printer .PrintNormal () it breaks and throws a POSControlException, and the text in it reads "An attempt was made to access a device of exclusive use, which must be declared before the action of a method or property can be used."

I seem to be doing something wrong.