or use windows provider: this is the vb code,

could you help to convert it to c# code?

Const ADS_UF_PASSWD_CANT_CHANGE = &H40

Function UserCannotChangePassword(strDomain As String, strUser As String, strUserCred As String, strPassword As String) As Boolean

UserCannotChangePassword = False

Dim oUser As IADs

strPath = "WinNT://" + strDomain + "/" + strUser

If "" <> strUserCred Then

Dim dso As IADsOpenDSObject

' Bind to the group with the specified user name and password.

Set dso = GetObject("WinNT:")

Set oUser = dso.OpenDSObject(strPath, strUserCred, strPassword, 1)

Else

' Bind to the group with the current credentials.

Set oUser = GetObject(strPath)

End If

If (oUser.Get("userFlags") And ADS_UF_PASSWD_CANT_CHANGE) <> 0 Then

UserCannotChangePassword = True

Else

UserCannotChangePassword = False

End If

End Function