Problem Calling Marshal Visual Basic 2012

[Renaldo9301]

Code:
#Region "Using Proxy"
<Runtime.Intero pServices.DllIm port("wininet.d ll", SetLastError:=T rue)> _
Private Shared Function InternetSetOpti on(ByVal hInternet As IntPtr, ByVal dwOption As Integer, ByVal lpBuffer As IntPtr, ByVal lpdwBufferLengt h 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_T YPE_PROXY As Integer = 3

Dim struct_IPI As Struct_INTERNET _PROXY_INFO

struct_IPI.dwAc cessType = INTERNET_OPEN_T YPE_PROXY
struct_IPI.prox y = Marshal.StringT oHGlobalAnsi(st rProxy)
struct_IPI.prox yBypass = Marshal.StringT oHGlobalAnsi("l ocal")

Dim intptrStruct As IntPtr = Marshal.AllocCo TaskMem(Marshal .SizeOf(struct_ IPI))

Marshal.Structu reToPtr(struct_ IPI, intptrStruct, True)

Dim iReturn As Boolean = InternetSetOpti on(IntPtr.Zero, INTERNET_OPTION _PROXY, intptrStruct, System.Runtime. InteropServices .Marshal.SizeOf (struct_IPI))
End Sub
#End Region