Error 997 occurred when using LsaOpenPolicy

[Eleanor]

Hi, all
I got the error 997 (Overlapped I/O operation is in progress.) when using LsaOpenPolicy.
Would someone be kind to help me figure it out?

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Here are the declarations
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<StructLayout(LayoutKind.Sequential, _
CharSet:=CharSet.Unicode)> _
Public Structure LSA_UNICODE_STRING
Dim Length As Integer
Dim MaximumLength As Integer
Dim Buffer As IntPtr
End Structure
<StructLayout(LayoutKind.Sequential, _
CharSet:=CharSet.Unicode)> _
Public Structure LSA_OBJECT_ATTRIBUTES
Dim Length As Integer
Dim RootDirectory As IntPtr
Dim ObjectName As LSA_UNICODE_STRING
Dim Attributes As Integer
Dim SecurityDescriptor As IntPtr
Dim SecurityQualityOfService As IntPtr
End Structure
<DllImport("Advapi32.dll", _
CharSet:=CharSet.Unicode, _
SetLastError:=True)> _
Public Shared Function LsaOpenPolicy( _
<[In]()> ByRef SystemName As LSA_UNICODE_STRING, _
<[In]()> ByRef ObjectAttributes As LSA_OBJECT_ATTRIBUTES, _
<[In]()> ByVal DesiredAccess As Integer, _
<[In](), Out()> ByRef PolicyHandle As IntPtr) As Integer
End Function
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and the calling part
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Dim ret As Integer
Dim SystemName As LSA_UNICODE_STRING
Dim ObjectAttr As New LSA_OBJECT_ATTRIBUTES
Dim Access As Integer = POLICY_ALL_ACCESS
Dim Policy As IntPtr
ObjectAttr.Length = 0
ret = LsaOpenPolicy( _
SystemName, _
ObjectAttr, _
Access, _
Policy)
If (ret <> 0) Then
Console.WriteLine(Marshal.GetLastWin32Error())
End If
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Thanks