Using DLL from a fingerprint detector in my VB

[emitojleyes]

Hi everyone!
i'm new at this forum as well as programming in .net
I have to develop a module that can use and configure a fingerprint detector; its documentation is written in C, as you will see below.
This is the function declaration that appears at the documentation
extern int WINAPI Wis_Diagnose (unsigned char *pwd, SYSTEMDATA
CurSystemData);
This function is for the device test. Ex, PC test if the device is ready.
It returns 0 if the device test is OK; -1 if the device test is NG

Below i write down the two structures that this function uses, as described in the manual:

typedef struct _SYSTEMDATA 
{ 
 unsigned char Version;  //DSP version 
 unsigned char IP[4];   //IP address 
 unsigned char NetMask[4];  //netmask 
 unsigned char Gateway[4];  //gateway 
 unsigned char BaudRate;  //baudrate for external 
 unsigned char DeviceID[3];  //device ID 
 unsigned short UserNo;  //user number 
 unsigned long LogNo;  //log number 
 unsigned char AuthenMode;  //1: 1-1  2: 1:1/1:N(<50 user
 unsigned char UartMode;  //1:232, 2:485 
 unsigned char VoiceEN;  //1:enable 
 unsigned char ServerIP[3][4]; //server IP sets 
 unsigned char IDLength;  //ID length for display 
 unsigned char Reserved[20]; 
   
  DOORDATA  DoorData;  //door setting 
 
  unsigned char DeviceName[16];  //device name 
  unsigned char HasDevice;    //this parameter should be 3 
  unsigned char ProtocolPswd;  //protocol password 
  unsigned char Reserved1[7]; 
}SYSTEMDATA; //112 Bytes 

//door data structure 
typedef struct _DOORDATA 
{ 
  unsigned short DoorOpenSec; 
  unsigned short DoorOverSec; 
  unsigned short AlarmTime; 
  unsigned char AlarmEnable;  //0: Disable 
  unsigned char Reserved[9]; 
}DOORDATA; //16 bytes

Now, i have been trying to define some variables that match the ones originally in the manual; below is this code:

Structure doordata
Dim DoorOpenSec As Short
Dim DoorOverSec As Short
Dim AlarmTime As Short
Dim AlarmEnable As String
Dim Reserved As String
End Structure

Structure SystemData
Dim Version As String
Dim IP As String
Dim NetMask As String
Dim Gateway As String
Dim BaudRate As String
Dim DeviceID As String
Dim UserNo As Short
Dim LogNo As Long
Dim AuthenMode As String
Dim UartMode As String
Dim VoiceEN As String
Dim ServerIP() As String
Dim IDLength As String
Dim Reserved As String
Dim DoorData As doordata
Dim DeviceName As String
Dim HasDevice As String
Dim ProtocolPswd As String
Dim Reserved1 As String
End Structure

And the DLLImport i declared is as follows:
<DllImport("C:\WisClient.dll", EntryPoint:="Wis_Diagnose", SetLastError:=True, _ 
CharSet:=CharSet.Unicode, ExactSpelling:=True, _
CallingConvention:=CallingConvention.StdCall)> _
Public Shared Function Diagnostico( _
ByVal pwd As String, _
ByRef systemdata As SystemData) _
As Integer
End Function

Now, sometimes, i got the folowing error:
PInvokeStackImbalance was detected
Message: A call to PInvoke function ....' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature.

And sometimes my Vstudio doesn't respond....

I will really appreciate any comments that can help me solve this problems
Thanks in advance!!

EMilio Leyes
Salta, ARgentina