BUG: Closing Two MDI Child Forms Rapidly Results in an Invalid Page Fault (257778)

SYMPTOMS

If you have a Visual Basic 6.0 Service Pack 3 multiple-document interface (MDI) project and you close two MDI Child Forms in rapid succession, you can cause the following Invalid Page Fault (IPF) error message to occur:

VB6 caused an invalid page fault in
module VB6.EXE at 0137:00420268.

Followed by this error message:

VB6 caused an invalid page fault in
module SSSCC.DLL at 0137:60567702.

The problem only happens in the Visual Basic Integrated Development Environment (IDE) on Microsoft Windows 95, and not as a compiled executable.

STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article. This bug was corrected in the latest service pack for Visual Studio 6.0.

For additional information about Visual Studio service packs, click the following article numbers to view the articles in the Microsoft Knowledge Base:

194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

194295 HOWTO: Tell That a Visual Studio Service Pack Is Installed

To download the latest Visual Studio service pack, visit the following Microsoft Web site:

http://msdn.microsoft.com/vstudio/downloads/updates/

MORE INFORMATION

Steps to Reproduce Behavior

Start a new Standard EXE project in Visual Basic. Form1 is created by default.
From the Project menu, add a new MDI form, a new Form, a new Class Module, and a new UserControl object to the project.
On the Project menu, and click to select Project1 Properties. On the General tab, set the Startup Object to MDIForm1.
With MDIForm1 visible, go to the Tools menu, and click to select the Menu Editor. Create one new menu item with the following properties:
Caption Load Forms
Name mnuLoadForms
Set Form1 and Form2's MDIChild Property = True.
On the Project menu, click to select Components. Select Microsoft Windows Common Controls 6.0 and click OK.
Add a Toolbar control to UserControl1.
Right-click on Toolbar1 and select Properties. Select the Buttons tab, and click Inset Button to add a new button to Toolbar1. Set the Caption Property to Exit.
Close the design window for the UserControl and place an instance of UserControl1 on Form1 and Form2.

Paste the following code into MDIForm1:

Option Explicit

Private Sub mnuLoadForms_Click()
    
    Form1.Show
    Form2.Show
    
End Sub

Paste the following code into the code windows of Form1 and Form2:

Option Explicit

Implements Class1

Private Sub Class1_UnloadForm()
    
    Unload Me
    
End Sub

Private Sub Form_Load()

    UserControl11.AddControl Me

End Sub

Paste the following code into Class1:

Option Explicit

Public Sub UnloadForm()
'
End Sub

Paste the following code into UserControl1:

Option Explicit

Private ucCollection As Collection

Public Sub AddControl(Item As Class1)
    
    ucCollection.Add Item
    
End Sub

Private Sub Toolbar1_ButtonClick(ByVal Button As MSComctlLib.Button)
Dim cls As New Class1

    Set cls = ucCollection.Item(1)

    cls.UnloadForm

    Set cls = Nothing
    
End Sub

Private Sub UserControl_Initialize()
    
    Set ucCollection = New Collection
    
End Sub

Private Sub UserControl_Terminate()

    Set ucCollection = Nothing

End Sub

Save and run the project. Select the Load Forms menu to load Form1 and Form2. Then click on the Exit button on both forms in rapid succession. You should see the IPF that is listed in the "Symptoms" section of this article.