some question about activex ,thread and event

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C++

ahh,its so bad a week,i can't get the way. Plz,someone help .

i create a simple object using atl(vs2005).code like：

DWORD WINAPI IPEventProc( LPVOID lpParameter)
{
   OVERLAPPED overlap;
   DWORD ret;
   HANDLE handle;
   handle=NULL;
   overlap.hEvent = WSACreateEvent()；
   ret = NotifyAddrChange(&handle, &overlap);
   if(WaitForSingleObject(overlap.hEvent, INFINITE) == WAIT_OBJECT_0 )	
   {
      //here trigger event
      Fire_IPChange(L"darling , i'm coming...");
 
   }
   
}
StartNotifyAddrChange(VARIANT_BOOL* bSucc)
{
  ...
  CreateThread(NULL,0,IPEventProc,0,CREATE_SUSPENDED,&tid);
  SetThreadPriority(tHandle,THREAD_PRIORITY_IDLE);
  ResumeThread(tHandle);
  ...
}

when i use this object in c#,it has this problem:

//deal the ip change event 
void ipobj_IPChange(string para)
{        
            
      MessageBox.Show(s);              //the first line
      textBox14.Text = "change";       //the second line             
            
}

when ip changed ,the first line can run correctly. but the second line runs nothing ,just nothing happend ,why ?

when only the first line ,it's ok!

when only the second line ,it's not work.

Please,give me some advice.

[edit]Code block added - OriginalGriff[/edit]