[求助]vb.net 里这个错误是怎么回事啊？

evaporated

   vb.net中的object reference not set to an instance of an object

错误，代码如下：

imports System.Runtime.InteropServices
   <StructLayout(LayoutKind.sequential)> structure PT_DioWriteBit
   ......
   end structure

   private lpDioWritePort As PT_DioWritePortByte

   Declare Function DRV_DioWriteBit Lib "adsapi32.dll"
   (ByVal DriverHandle As integer,byref DioWriteBit As PT_DioWriteBit) As
                                                                      integer

   Dim ptDioWriteBit As New PT_DioWriteBit
            ptDioWriteBit.Port = 0
            ptDioWriteBit.bit = 1
            ptDioWriteBit.state = 1

            Dim newClass1 As New class1
            errCde = newClass1.DRV_DioWriteBit(deviceHandle, ptDioWriteBit)

errCde为整型

到这里调用函数DRV_DioWriteBit时，出现该错误。

 object reference not set to an instance of an object

请教各位大虾，这是为什么啊？

在vb中的类似代码是没问题的。