Problem Calling Marshal Visual Basic 2012

[Renaldo9301]

Code:
#Region "Using Proxy"
<Runtime.InteropServices.DllImport("wininet.dll" , SetLastError:=True)> _
Private Shared Function InternetSetOption(ByVal hInternet As IntPtr, ByVal dwOption As Integer, ByVal lpBuffer As IntPtr, ByVal lpdwBufferLength As Integer) As Boolean
End Function

Public Structure Struct_INTERNET_PROXY_INFO
Public dwAccessType As Integer
Public proxy As IntPtr
Public proxyBypass As IntPtr
End Structure

Public Sub UseProxy(ByVal strProxy As String)
Const INTERNET_OPTION_PROXY As Integer = 38
Const INTERNET_OPEN_TYPE_PROXY As Integer = 3

Dim struct_IPI As Struct_INTERNET_PROXY_INFO

struct_IPI.dwAccessType = INTERNET_OPEN_TYPE_PROXY
struct_IPI.proxy = Marshal.StringToHGlobalAnsi(strProxy)
struct_IPI.proxyBypass = Marshal.StringToHGlobalAnsi("local")

Dim intptrStruct As IntPtr = Marshal.AllocCoTaskMem(Marshal.SizeOf(struct_IPI))

Marshal.StructureToPtr(struct_IPI, intptrStruct, True)

Dim iReturn As Boolean = InternetSetOption(IntPtr.Zero, INTERNET_OPTION_PROXY, intptrStruct, System.Runtime.InteropServices.Marshal.SizeOf(stru ct_IPI))
End Sub
#End Region