hContext in SCradEstablishContext function take -ve value in 64bit

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VB

64-bit

I have a code .

Dim hContext As IntPtr
Dim rc As IntPtr
Dim dwScope As Integer

Dim mszReaders(512) As Byte
Dim mszGroup(512) As Byte
Dim pcchReaders As Long

Dim curReader As String

' if a Context is established, release it first
If isContext = True Then RELCONTEXTBUTTON_Click(RELCONTEXTBUTTON, New System.EventArgs())

' Set Scope (see Scard.bas "Scopes")
dwScope = SCARD_SCOPE_USER

' Establish Context
rc = SCardEstablishContext(dwScope, 0, 0, hContext)
If rc <> OKERR_OK Then
    MESSAGETEXT.Text = (HandleError(rc))
    Exit Sub
End If

' Set maximum Length of mszReaders
pcchReaders = 2048

' Create a Multistring (terminated with two '\0's)
mszGroup(0) = &H0
mszGroup(1) = &H0
Try
    rc = SCardListReaders(hContext, mszGroup(LBound(mszGroup)), mszReaders(LBound(mszReaders)), pcchReaders)
Catch ex As Exception
    MessageBox.Show(ex.Message)

End Try

But when I execute this code on x86bit,Its work fine and value of hContext is +ve(&HCD010000) .but when I execute it on x64bit
the hContext take the -ve value(&HCD00000100000000).When I debug the code "SCardListReaders" gives "Stack Overflow Exception".
So what should be the datatype for hContext and how to remove this error