Invalid Parameter: Name handle Exception

[Palash Aich]

I am using VB.Net code to print barcode label in Zebra TLP 2844 printer. And the printer is connected to system by USB port. When i execute the code i get an error "Invalid Parameter : Name handle" in the line outFile = New FileStream(_SafeFileHandle, FileAccess.Write) . Can you please help me to rectify this.
As this is a USB port So i shared the printer and used the UNC path. But still i get the error. Below is the complete code


Name Spaces
Imports System.IO
Imports System.Runtime.InteropServices

Here is the button click code

Dim _print as new ZebraPrint
_print.StartWrite("//ComputerName/PrinterSharedName")
dim _Text as String = "Print test"
_print.Write("A30,120,0,4,2,1,N,""" & _Text & """")
_print.EndWrite()




Class


Public Class ZebraPrint
#Region " Private constants "
Private Const GENERIC_WRITE As Integer = &H40000000
Private Const OPEN_EXISTING As Integer = 3
#End Region

#Region " Private members "
Private _SafeFileHandle As Microsoft.Win32.SafeHandles.SafeFileHandle
Private _fileWriter As StreamWriter
Private _outFile As FileStream

#End Region

#Region " private structures "
<StructLayout(LayoutKind.Sequential)> _
Public Structure SECURITY_ATTRIBUTES
Private nLength As Integer
Private lpSecurityDescriptor As Integer
Private bInheritHandle As Integer
End Structure

#End Region

#Region " com calls "
Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Integer, ByVal dwShareMode As Integer, <MarshalAs(UnmanagedType.Struct)> ByRef lpSecurityAttributes As SECURITY_ATTRIBUTES, ByVal dwCreationDisposition As Integer, ByVal dwFlagsAndAttributes As Integer, ByVal hTemplateFile As Integer) As Microsoft.Win32.SafeHandles.SafeFileHandle

#End Region
#Region " Public methods "
Public Sub StartWrite(ByVal printerPath As String)
Dim SA As SECURITY_ATTRIBUTES

_SafeFileHandle = CreateFile(printerPath, GENERIC_WRITE, 0, SA, OPEN_EXISTING, 0, 0)

Try

_outFile = New FileStream(_SafeFileHandle, FileAccess.Write)

_fileWriter = New StreamWriter(_outFile)

Catch ex As Exception

System.Windows.Forms.MessageBox.Show("Can not find printer.", "Warning", Windows.Forms.MessageBoxButtons.OK, Windows.Forms.MessageBoxIcon.Error, Windows.Forms.MessageBoxDefaultButton.Button1)

End Try



End Sub



Public Sub Write(ByVal rawLine As String)

If _fileWriter IsNot Nothing Then

_fileWriter.WriteLine(rawLine)

End If

End Sub



Public Sub EndWrite()



If _fileWriter IsNot Nothing Then

_fileWriter.Flush()

_fileWriter.Close()

_outFile.Close()

End If

_SafeFileHandle.Close()

_SafeFileHandle.Dispose()



End Sub

#End Region



End Class

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