Stopping a Coroutine and drawing OnGUI

Hello, below is a code that I have for logging into a database. Everything works really well however I'm trying to get a pop up window to show to the user. Unfortunately, even though I have done pop up windows before, I'm a bit stuck. I can't seem to get it to show anything. The window simply won't show. That being said, I've tried doing this without canceling the coroutine and with canceling the coroutine all giving the same result. I also seem to be getting an error that states all GUI function calls must be in the OnGUI function. Which is weird because usually to make a pop up window you have to draw all the GUI components in a separate function from the OnGUI so I don't know why I'm getting all the errors. Any help would be greatly appreciated.

 using UnityEngine;
 using System.Collections;
 
 public class Login : MonoBehaviour {
 
  public Texture LoginBackground;
  public Texture2D stylebackground;
  public GUIStyle LoginStyle;
  public GUIStyle LoginTextBox;
  public GUIStyle LoginButton;
  public string Username;
  public string Password;
  public float transparent;
  private string url;
  public WWW w;
  public WWWForm loginform;
  public bool doWindow0 = false;
  public string formText;
  // Use this for initialization
  void Start () {
  LoginStyle.fontSize = 72;
  LoginStyle.alignment = TextAnchor.MiddleCenter;
  LoginTextBox.fontSize = 20;
  LoginTextBox.alignment = TextAnchor.MiddleCenter;
  LoginTextBox.normal.background = stylebackground;
  LoginButton.fontSize = 30;
  LoginButton.alignment = TextAnchor.MiddleCenter;
  loginform = new WWWForm();
  }
  
  // Update is called once per frame
  void Update () {
  doWindow0 = false;
  }
  
  void OnGUI() {
  GUI.backgroundColor = Color.black;
  GUI.DrawTexture(new Rect(0,0,Screen.width,Screen.height),LoginBackground,ScaleMode.StretchToFill, false, 0.0f);
  GUI.Label(new Rect(Screen.width/2-250,Screen.height/2-250,500,250),"Username:", LoginStyle);
  Username = GUI.TextField(new Rect(Screen.width/2-250,Screen.height/2-80,500,50), Username, 10, LoginTextBox);
  GUI.Label(new Rect(Screen.width/2-250,Screen.height/2-50,500,250),"Password:", LoginStyle);
  Password = GUI.TextField(new Rect(Screen.width/2-250,Screen.height/2+120,500,50), Password, 10, LoginTextBox);
  if (GUI.Button(new Rect(Screen.width/2-150,Screen.height/2+200,300,50),"Login:", LoginButton))
  {
  //CheckLogin();
  StartCoroutine(CheckLogin());
  }
  if (doWindow0 == true)
  {
  GUI.Window (0, new Rect (Screen.width/2-240,Screen.height/2-100,800,120), DoMyWindow, "Notice:");
  }
 
  }
  
  void DoMyWindow (int windowID) {
  GUI.Label(new Rect (10, 20, 800, 40), formText);
  if (formText == "Login success. Click the close button to continue to the character selection screen.")
  {
  if (GUI.Button (new Rect (10,80,100,20), "Close"))
  doWindow0 = false;
  Application.LoadLevel("CharacterSelect");
  }
  else
  {
  if (GUI.Button (new Rect (10,80,100,20), "Close"))
  {
  doWindow0 = false;
  } 
  }
 }
  
  IEnumerator CheckLogin()
  {
  url = "http://redlightlife.tk/scripts/checklogin.php?username=" + WWW.EscapeURL(Username) + "&password=" + WWW.EscapeURL(Password);
  w = new WWW(url);
  yield return w;
  Debug.Log("Downloaded");
  if (w.error != null)
  {
  print(w.error);
  }
  if (w.error == null)
  {
  formText = w.text;
  w.Dispose();
  print(formText);
  doWindow0 = true;
  print(doWindow0);
  StopAllCoroutines();
  }
  }
 }