Q170340: FIX: Debugging ActiveX Server in IDE Causes Application Error

Article: Q170340
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:5.0,6.0
Operating System(s): 
Keyword(s): kbVBp kbVBp500 kbVBp600 kbGrpDSVB kbDSupport
Last Modified: 10-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0, on platform(s):
   - the operating system: Microsoft Windows NT 
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0, on platform(s):
   - the operating system: Microsoft Windows NT 
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SYMPTOMS
========

When debugging an ActiveX server running in the Visual Basic IDE on Windows NT
4.0, you may receive the following error when the ActiveX server attempts to
return control back to the Client application running in a second Visual Basic
IDE:

  "Step Into: VB5.EXE - Application Error
  The instruction at <memory address> referenced memory at <memory
  address>. The memory could not be "read"

RESOLUTION
==========

To correct this problem, use one of the following methods.

- Install Windows NT Service Pack 2 or later. The system requirements on the
  Visual Basic Box recommend Service Pack 2 for Windows NT 4.0.

-or-

- Use late binding when creating the ActiveX server object.

STATUS
======

Microsoft has confirmed this to be a problem in the Microsoft products that are
listed at the beginning of this article.
This problem was corrected in Windows 2000.

MORE INFORMATION
================

A common method of debugging ActiveX servers is to run them in one session of
the Visual Basic IDE while the client runs in a second session of the Visual
Basic IDE. When using early binding to an ActiveX server on Windows NT 4.0, you
will receive an APPLICATION ERROR when the ActiveX server tries to return
control to the client application.

NOTE: This is a problem only if Windows NT Service Pack 2 or later is not
installed.

Steps to Reproduce Behavior
---------------------------

1. Create a new ActiveX EXE Project.

2. Name the Class "clsTest" (without the quotation marks).

3. Add the following code to the class module:

        Private Sub Class_Initialize()
           Debug.Print "Class Init"
        End Sub

4. Click Properties on the Project menu. On the General tab, set the Project
  name to "pjxTest." On the Make tab, set the Application Title to "pjxTest."
  On the Component Tab, set the Start Mode to ActiveX Component and click OK.

5. Run the ActiveX server by pressing CTRL+F5 or, from the Run Menu, select
  Start with Full Compile.

6. Start a second session of Visual Basic and create a Standard EXE project.

7. From the Project Menu, select References. Check "pjxTest" and click OK.

8. Place a CommandButton on Form1.

9. Add the following code to the form:

        Dim obj As pjxTest.clstest

        Private Sub Command1_Click()
           Set obj = New pjxTest.clstest
        End Sub

10. From the View Menu, select Toolbars, and make sure the Debug Toolbar is
  checked.

11. Use the Step Into button on the Debug Toolbar to step through the code. You
  will get an APPLICATION ERROR when you click the Step Into button and you
  are on the "End Sub" line in the Class_Initialize Sub of the ActiveX server.
  Because the APPLICATION ERROR is from the Client, the Client session of
  Visual Basic will be terminated.

Additional query words: OLE kbAutomation instance

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Keywords          : kbVBp kbVBp500 kbVBp600 kbGrpDSVB kbDSupport 
Technology        : kbVBSearch kbAudDeveloper kbPTNotAssigned kbZNotKeyword2
Version           : WINDOWS:5.0,6.0
Issue type        : kbbug
Solution Type     : kbfix

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