Convert c++ to vb.net

[crazyrunrun]

Hi,
I covert following code to vb.net

typedef struct {
BYTE sSerialNumber[SERIALNO_LEN];
BYTE byAlarmInPortNum;
BYTE byAlarmOutPortNum;
BYTE byDiskNum;
BYTE byDVRType;
BYTE byChanNum;
BYTE byStartChan;
}NET_DVR_DEVICEINFO, *LPNET_DVR_DEVICEINFO;

LONG NET_DVR_Login(char *sDVRIP,WORD wDVRPort,char *sUserName,char *sPassword,LPNET_DVR_DEVICEINFO lpDeviceInfo);

Public Structure LPNET_DVR_DEVICEINFO
 Public sSerialNumber() As Byte  'serial number
        Public byAlarmInPortNum As Byte 
        Public byAlarmOutPortNum As Byte 
        Public byDiskNum As Byte        
        Public byDVRType As Byte       
        Public byChanNum As Byte     
        Public byStartChan As Byte    
    End Structure
 
  <DllImport("HCNetSDK.dll")> Public Function NET_DVR_Login( _
   ByVal IPAddress() As Char, _
   ByVal DVRPort As UInt16, _
   ByVal UserName() As Char, _
   ByVal Password() As Char, _
   ByRef lpDeviceInfo As LPNET_DVR_DEVICEINFO) As <MarshalAs(I8)> Long
    End Function

When i call this function, always got error "Object reference not set to an instance of an object".
Anyone can help me. Thank you.