[Linker Error] Unresolved external

//---------------------------------------------------------------------------
 
#include <vcl.h>
#pragma hdrstop
 
#include "Main.h"
#include "SendMessage.h"
#include "ShowMessage.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma link "trayicon"
#pragma resource "*.dfm"
TMainForm *MainForm;
static AnsiString ComputerName;
static AnsiString Address;
static TListItem *LI;
static TStringList *UserList;
static AnsiString ADirectory;
//---------------------------------------------------------------------------
__fastcall TMainForm::TMainForm(TComponent* Owner)
        : TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::UDPServerUDPRead(TObject *Sender,TStream *AData, TIdSocketHandle *ABinding) {
     int Show;
     AnsiString Tmp,RemoteName,Message;
     TStringStream* SS=new TStringStream("");
     SS->CopyFrom(AData,AData->Size);
     Tmp=SS->DataString;
     RemoteName=Tmp.SubString(Tmp.Pos("(")+1,Tmp.Pos(")")-Tmp.Pos("(")-1);
     Show=1;
     if (Tmp.Pos("###Start###")!=0) {
        if (Tmp.Pos(ComputerName)==0) {
           if (MainForm->Active==True) {
              UDPServer->Send(ABinding->PeerIP,4000,"###Here And Active###("+ComputerName+")");
           } else {
              UDPServer->Send(ABinding->PeerIP,4000,"###Here And Inactive###("+ComputerName+")");
           }
           ChatInputOutput->Lines->Add("Подключился: "+RemoteName);
           UserList->Add(RemoteName);
           LI=UsersListView->Items->Add();
           LI->Caption=RemoteName;
           LI->ImageIndex=-1;
           LI->Indent=-1;
           LI->SubItems->Add("");
           LI->SubItemImages[0]=0;
           LI->SubItems->Add("\"Неактивен\"");
           MediaPlayer->FileName=ADirectory+"Start.wav";
           MediaPlayer->Open();
           MediaPlayer->Play();
        }
        Show=0;
     }
     if (Tmp.Pos("###Here And Active###")!=0) {
        if (Tmp.Pos(ComputerName)==0) {
           ChatInputOutput->Lines->Add("Уже в сети: "+RemoteName);
           UserList->Add(RemoteName);
           LI=UsersListView->Items->Add();
           LI->Caption=RemoteName;
           LI->ImageIndex=-1;
           LI->Indent=-1;
           LI->SubItems->Add("");
           LI->SubItemImages[0]=0;
           LI->SubItems->Add("\"Активен\"");
        }
        Show=0;
     }
     if (Tmp.Pos("###Here And Inactive###")!=0) {
        if (Tmp.Pos(ComputerName)==0) {
           ChatInputOutput->Lines->Add("Уже в сети: "+RemoteName);
           UserList->Add(RemoteName);
           LI=UsersListView->Items->Add();
           LI->Caption=RemoteName;
           LI->ImageIndex=-1;
           LI->Indent=-1;
           LI->SubItems->Add("");
           LI->SubItemImages[0]=0;
           LI->SubItems->Add("\"Неактивен\"");
        }
        Show=0;
     }
     if (Tmp.Pos("###Stop###")!=0) {
        if (Tmp.Pos(ComputerName)==0) {
           ChatInputOutput->Lines->Add("Отключился: "+RemoteName);
           if (UserList->IndexOf(RemoteName)!=-1) {
              UsersListView->Items->Delete(UserList->IndexOf(RemoteName));
              UserList->Delete(UserList->IndexOf(RemoteName));
           }
        }
        Show=0;
     }
     if (Tmp.Pos("###Active###")!=0) {
        if (Tmp.Pos(ComputerName)==0) {
           if (UserList->IndexOf(RemoteName)!=-1) {
              LI=UsersListView->Items->Item[UserList->IndexOf(RemoteName)];
              LI->SubItems->Strings[1]="\"Активен\"";
           }
        }
        Show=0;
     }
     if (Tmp.Pos("###Inactive###")!=0) {
        if (Tmp.Pos(ComputerName)==0) {
           if (UserList->IndexOf(RemoteName)!=-1) {
              LI=UsersListView->Items->Item[UserList->IndexOf(RemoteName)];
              LI->SubItems->Strings[1]="\"Неактивен\"";
           }
        }
        Show=0;
     }
     if (Tmp.Pos("###Activate###")!=0) {
        TrayIcon->Restore();
        MediaPlayer->FileName=ADirectory+"Call.wav";
        MediaPlayer->Open();
        MediaPlayer->Play();
        Show=0;
     }
     if (Tmp.Pos("###ChatMessage###")!=0) {
        Message=Tmp.SubString(Tmp.Pos(")")+2,Tmp.Length()-Tmp.Pos(")")-1);
     }
     if (Tmp.Pos("###PrivateMessage###")!=0) {
        Message=Tmp.SubString(Tmp.Pos(")")+2,Tmp.Length()-Tmp.Pos(")")-1);
        SS->Position=0;
        SS->WriteString(Message);
        SS->Position=0;
        ShowMessageForm->MessageOutput->Lines->LoadFromStream(SS);
        TrayIcon->Restore();
        MediaPlayer->FileName=ADirectory+"Message.wav";
        MediaPlayer->Open();
        MediaPlayer->Play();
        ShowMessageForm->ShowModal();
        Show=0;
     }
     if (Show==1) {
        ChatInputOutput->Lines->Add(RemoteName+": "+Message);
     }
     if (UsersListView->Items->Count>0) {
        TrayIcon->IconIndex=0;
     } else {
        TrayIcon->IconIndex=1;
     }
     delete SS;
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::SendBtnClick(TObject *Sender) {
     UDPServer->Broadcast("###ChatMessage###("+ComputerName+") "+MessageInput->Text,4000);
     MessageInput->Text="";
     MessageInput->SetFocus();
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::FormClose(TObject *Sender, TCloseAction &Action) {
     UDPServer->Broadcast("###Stop###("+ComputerName+")",4000);
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::ApplicationEventsException(TObject *Sender, Exception *E) {
     Application->MessageBox("","",MB_OK);
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::ApplicationEventsActivate(TObject *Sender) {
     UDPServer->Broadcast("###Active###("+ComputerName+")",4000);
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::ApplicationEventsDeactivate(TObject *Sender) {
     UDPServer->Broadcast("###Inactive###("+ComputerName+")",4000);
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::ChatInputOutputEnter(TObject *Sender) {
     MessageInput->SetFocus();
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::UsersListViewEnter(TObject *Sender) {
     MessageInput->SetFocus();
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::UsersListViewContextPopup(TObject *Sender, TPoint &MousePos, bool &Handled) {
     if (UsersListView->ItemIndex!=-1) {
        PopupMenu->Popup(MainForm->Left+UsersListView->Left+MousePos.x,MainForm->Top+UsersListView->Top+MousePos.y+50);
     }
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::ApplicationEventsMinimize(TObject *Sender) {
     TrayIcon->Minimize();
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::CallMenuItemClick(TObject *Sender) {
     UDPServer->Send(UsersListView->Selected->Caption,4000,"###Activate###("+ComputerName+")");
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::SendMenuItemClick(TObject *Sender) {
     int i,Result;
     TStringStream *Message=new TStringStream("");
     SendMessageForm->UserSelect->Clear();
     SendMessageForm->UserSelect->Items->Add("<Всем пользователям>");
     for (i=1;i<=UserList->Count;i++) {
         SendMessageForm->UserSelect->Items->Add(UserList->Strings[i-1]);
     }
     SendMessageForm->UserSelect->ItemIndex=UsersListView->ItemIndex+1;
     Result=SendMessageForm->ShowModal();
     if (Result==1) {
         SendMessageForm->MessageInput->Lines->SaveToStream(Message);
         Message->Position=0;
         if (SendMessageForm->UserSelect->ItemIndex==0) {
            UDPServer->Broadcast("###PrivateMessage###("+ComputerName+") "+Message->DataString,4000);
         } else {
            UDPServer->Send(UserList->Strings[SendMessageForm->UserSelect->ItemIndex-1],4000,"###PrivateMessage###("+ComputerName+") "+Message->DataString);
         }
     }
     delete Message;
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::FormCreate(TObject *Sender) {
     UserList=new TStringList();
     ComputerName="qwerty";
     UDPServer->Broadcast("###Start###("+ComputerName+")",4000);
     ADirectory=Application->ExeName.SubString(1,Application->ExeName.LastDelimiter("\\"));
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::FormDestroy(TObject *Sender) {
     delete UserList;
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::TrayIconRestore(TObject *Sender) {
     MainForm->Show();
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::ExitMenuItemClick(TObject *Sender) {
     UDPServer->Broadcast("###Stop###("+ComputerName+")",4000);
     Application->Terminate();
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::SendAllMenuItemClick(TObject *Sender) {
     int i,Result;
     TStringStream *Message=new TStringStream("");
     SendMessageForm->UserSelect->Clear();
     SendMessageForm->UserSelect->Items->Add("<Всем пользователям>");
     for (i=1;i<=UserList->Count;i++) {
         SendMessageForm->UserSelect->Items->Add(UserList->Strings[i-1]);
     }
     SendMessageForm->UserSelect->ItemIndex=0;
     Result=SendMessageForm->ShowModal();
     if (Result==1) {
         SendMessageForm->MessageInput->Lines->SaveToStream(Message);
         Message->Position=0;
         if (SendMessageForm->UserSelect->ItemIndex==0) {
            UDPServer->Broadcast("###PrivateMessage###("+ComputerName+") "+Message->DataString,4000);
         } else {
            UDPServer->Send(UserList->Strings[SendMessageForm->UserSelect->ItemIndex-1],4000,"###PrivateMessage###("+ComputerName+") "+Message->DataString);
         }
     }
     delete Message;
}
//---------------------------------------------------------------------------
void __fastcall TMainForm::MediaPlayerNotify(TObject *Sender) {
     MediaPlayer->Close();
}
//---------------------------------------------------------------------------