public class BeholdRC
   {
      public static IntPtr hLib = Imports.LoadLibrary("BeholdRC.dll");
      public static IntPtr GetCardCount = Imports.GetProcAddress(hLib, "GetCardCount");
      public static IntPtr OpenCard = Imports.GetProcAddress(hLib, "OpenCard");
      public static IntPtr GetRemoteCode = Imports.GetProcAddress(hLib, "GetRemoteCode");
      public static IntPtr GetRemoteCodeEx = Imports.GetProcAddress(hLib, "GetRemoteCodeEx");
      public static IntPtr UnInit = Imports.GetProcAddress(hLib, "UnInit");

      public static bool init;

      public BeholdRC()
      {
         init = false;

         if(GetCardCount == null || OpenCard == null || GetRemoteCode == null || UnInit == null) // GetRemoteCodeEx may be absent in library. Don't check for it.
         {
            Imports.FreeLibrary(hLib);
         }
      }
      public void Dispose()
      {
            Imports.FreeLibrary(hLib);
      }
   }

#region Delegates

   //  Объявляем делегаты, к которым будет приводиться нужная неуправляемая функция
   public delegate int GetCardCountInvoker();
   public delegate bool OpenCardInvoker();
   public delegate int GetRCCodeInvoker();
   public delegate ulong GetRCCodeExInvoker();

#endregion

#region Import
   
   /// <summary>
   /// Импорт необходимых функций Windows API
   /// Смотрите также документацию по атрибуту DllImportAttribute
   /// http://msdn.microsoft.com/library/rus/default.asp?url=/library/rus/cpref/html/frlrfsystemruntimeinteropservicesdllimportattributememberstopic.asp
   /// </summary>
   public class Imports
   {
      [DllImport("kernel32.dll")]
      public static extern IntPtr LoadLibrary(string lpFileName);

      [DllImport("kernel32.dll", CharSet = CharSet.Ansi, ExactSpelling = true)]
      public static extern IntPtr GetProcAddress(IntPtr hModule, string procName);

      [DllImport("kernel32.dll", SetLastError = true)]
      public static extern bool FreeLibrary(IntPtr hModule);
   }

   #endregion

#region Implemented Methods
      
      public static int BTV_SelectCard()
      {
         return BTV_SelectCard(0);
      }

      public static int BTV_SelectCard(int idx)
      {
         int i;
         int cnt;

         GetCardCountInvoker cardCountInvoker = Marshal.GetDelegateForFunctionPointer(BeholdRC.GetCardCount, typeof(GetCardCountInvoker)) as GetCardCountInvoker;
         OpenCardInvoker opencardInvoker =  Marshal.GetDelegateForFunctionPointer(BeholdRC.OpenCard, typeof(OpenCardInvoker)) as OpenCardInvoker;
      
         if(idx >= 0 && BeholdRC.hLib != null)
         {
            cnt = cardCountInvoker();

            if(cnt > idx)
            {
               for(i = 0; i < cnt; ++i)
               {
                  if(opencardInvoker())
                  {
                     if(idx == 0)
                     {
                        BeholdRC.init = true;
                        return 1;
                     }
                     --idx;
                  }
               }
            }
         }

         BeholdRC.init = false;

         return 0;
      }
#endregion

opencardInvoker()

public delegate bool OpenCardInvoker(ulong index);

typedef BOOL  (__cdecl OPENCARD) (IN ULONG ulCardIdx);

IN ULONG ulCardIdx

A call to PInvoke function 'IRControlTool!IRControlTool.OpenCardInvoker::Invoke' 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.

textBoxLog.Text = String.Concat(BeholdRcWrapper.BeholdRcWrapper.GetDeviceNameA(0), "\r\n");

[DllImport("BeholdRC.dll", SetLastError = true)]
public static extern string GetDeviceNameA(int card);

PInvokeStackImbalance was detected
Message: A call to PInvoke function 'BeholdRcWrapper!BeholdRcWrapper.BeholdRcWrapper::OpenCard' 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.

[DllImport("BeholdRC.dll", CallingConvention=CallingConvention.Cdecl, SetLastError = true)]