EntryPointNotFoundException, when trying to import DLL. Help please :)

Hi all, I'm having some errors with a DLL I created but I don't know why...

This is the error:

 EntryPointNotFoundException: text2Speech
 TTSFestival.OnMouseUp () (at Assets/Scripts/TTSFestival.cs:20)
 UnityEngine.SendMouseEvents:DoSendMouseEvents()

This my script:

 using UnityEngine;
 using System;
 using System.Collections;
 using System.Runtime.InteropServices;
 
 public class TTSFestival : MonoBehaviour 
 {
     //[DllImport ("TTSPlugin", EntryPoint="text2Speech")] private static extern int    text2Speech(string message, string voice);
     [DllImport ("TTSPlugin")]    private static extern void text2Speech(string message, string voice);
 
     public string voice = "english"; 
     public string message ="Text";
 
     void OnMouseUp () {
         text2Speech(message, voice);
     }
 }

And this my DLL code:

 #if _MSC_VER // this is defined when compiling with Visual Studio
 #define EXPORT_API __declspec(dllexport) // Visual Studio needs annotating exported functions with this
 #else
 #define EXPORT_API // XCode does not need annotating exported functions, so define is empty
 #endif
 
 // ------------------------------------------------------------------------
 // Plugin itself
 
 #include <sstream>
 #include <string>
 
 // Link following functions C-style (required for plugins)
 extern "C"
 {
     void EXPORT_API text2Speech(std::string message, std::string voice)
     {
         std::stringstream commandoss;
         std::string commandos,msg;
         commandoss << "start /B festival.exe --libdir \"festival/lib\" "; 
                     
         commandoss << voice;
            
         commandoss << " -A -T \"";
            
         msg=message;//.toStdString();
         //std::replace_if(msg.begin(),msg.end(),boost::is_any_of("\""),', ');
         commandoss << msg;
         commandoss << "\"";
         commandos = commandoss.str();
            
         system(commandos.c_str());      
     }   
 
 } // end of export C block

Any kind of help is welcomed :))