Error when using GetParent()

Hi everybody,
I stumbled on a little error that is confusing.
My program uses tabs to control two dialog boxes each having their own classes and functions. I instantiate them as follows:

Code:

if(GetCurSel() == 0) {
 if (theDialog1 != NULL) {
  theDialog1->SetFocus();
 }
 else {
  theDialog1 = new dialog1;
  theDialog1->Create(IDD_DIALOG1,this);
 }

I also have some code that listens to messages from the dialog box and sets theDialog1 pointer appropriately:

Code:

ON_MESSAGE(WM_USER_DIALOG_DESTROYED, OnDialogDestroyed)

LRESULT tabControl::OnDialogDestroyed (WPARAM wParam, LPARAM lParam)
{
	theDialog1 = NULL;
	return 0;
}

In my Dialog1 class, I have this code for sending the message to the parent that instantiated an instance of this class when someone clicks on the ESC key:

Code:

// dialog1 message handlers
void dialog1::PostNcDestroy()
{ 
	CDialog::PostNcDestroy();
	CWnd* pWindow = GetParent();
	//AfxGetMainWnd()->
	pWindow->SendMessage (WM_USER_DIALOG_DESTROYED, 0, 0);
	delete this;
}

void dialog1::OnCancel()
{
	DestroyWindow();
}

Alas everytime the program reaches the line CWnd* pWindow = GetParent();
it crashes and gives me a debug assertion failed error.
Can anybody look at the code and let me know what I am doing wrong. Also if I use AfxGetMainWnd()-> it works fine but the class that instantiated the dialog window does not seem to get the message properly. I am thinking it's because it is not the main window. Can someone confirm this. Thanks
Amish

I figured out that I was not passing the parent window when constructing the dialog1 instance. After that it works fine.